Evaluating the impacts of climate change and land-use change on future droughts in northeast Thailand.

The impacts of climate change (CC) on droughts are well documented, but the effects of land-use change (LUC) are poorly understood. This study compares the projected individual and combined impacts of these stressors on future droughts (2021-2050), with respect to baseline (1981-2010) in one of the major tributaries of the Mekong River. LUC impacts on hydrological droughts are minimal compared to CC, with the latter expected to shorten the recurrence interval of a 20-year return period event to every 14 years. Both CC and LUC have significant impacts on agricultural droughts with heightened sensitivity. 'Once in a Decade' agricultural droughts will be 40% (35%) longer and 88% (87%) more severe under the CC (LUC) scenario. Under both stressors, the events occurring every 20 years will be twice as frequent. Results highlight the intensification of future droughts and the urgency for actions to mitigate/adapt to climate change and manage land use. Future policy shall holistically address agricultural water management, sustainable land use management, and crop management to cope with future droughts. We recommend developing resilient agricultural practices, enhanced water resource management strategies, and incorporating drought risk into land-use planning to mitigate the compounded impacts of CC and LUC.

Evaluating aquifer stress and resilience with GRACE information at different spatial scales in Cambodia.

Groundwater exploitation for different sectors in Cambodia is expanding. Groundwater levels have already begun to decline in some parts of the country. Monitoring and assessing groundwater storage (GWS) change, aquifer stress and aquifer resilience will support the proper planning and management of the country's groundwater resources; however, information regarding groundwater in Cambodia is currently scarce. Thus, GWS change in Cambodia over the 15 years from April 2002 to March 2017 was assessed using remote-sensing-based Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) datasets, with a comprehensive validation of the GRACE-derived groundwater storage anomaly (GWSA) with respect to in-situ field-based observations. The current study also investigated the impact of surface water storage (SWS) change in Tonle Sap Lake, South-East Asia's largest freshwater lake, on deriving the GWS change in Cambodia. The groundwater aquifer stresses (GAS), and aquifer resilience (AR) were also evaluated. The validation results were promising, with the correlation coefficient between satellite-based estimations and ground-based measurements ranging from 0.82 to 0.88 over four subbasins. The overall decreasing rate of GWS was found to be -0.63 mm/month, with two basins having the highest declining rate of more than 1.4 mm/month. Meanwhile, the aquifer experiencing stress during the dry season had a very low ability to quickly recover from these stresses. These findings emphasise that appropriate management is urgently needed to ensure the sustainability of the groundwater resource system in this country. Supplementary Information: The online version contains supplementary material available at 10.1007/s10040-022-02570-w.

L'exploitation des eaux souterraines s'étend au Cambodge dans différents secteurs. Les niveaux piézométriques ont déjà commencé à baisser sur quelques secteurs du pays. Surveiller et évaluer les changements de stock d'eau souterraine (GWS), la pression sur les aquifères et leur résilience supportera une planification et gestion correctes des ressources en eau dans le pays; toutefois, les informations en relation avec les eaux souterraines sont peu nombreuses aujourd'hui au Cambodge. Ainsi, les changements de GWS au Cambodge sur les 15 dernières années, d'avril 2002 à mars 2017 ont été évalués à l'aide des méthodes de télédétection basées sur le Gravity Recovery and Climate Experiment (GRACE) et les jeux de données du Global Land Data Assimilation System (GLDAS) avec une validation complète des anomalies de stockage d'eau souterraine (GWSA) de GRACE par l'utilisation d'observations de terrain. L'étude a également permis d'étudier l'impact des changements de stocks d'eau de surface (SWS) dans le lac Tonle Sap, le plus grand lac d'eau douce du sud-est asiatique, par dérivation des changements de GWS au Cambodge. Les pressions sur les eaux souterraines (GAS) et la résilience des aquifère (AR) ont également été évaluées. La validation des résultats est prometteuse, avec un coefficient de corrélation entre les estimations basées sur les données satellitaires et les mesures de terrain allant de 0.82 à 0.88 sur quatre sous-bassins. Un taux de baisse globale du GWS de ­0.63 mm/mois a été estimé, avec deux sous-bassins ayant des baisses plus fortes de plus de 1.4 mm/mois. Sur la même période, les aquifère qui subissent un stress durant les basses eaux montrent une faible capacité à récupérer de ce stress. Ces résultats montrent qu'une gestion adéquate est urgemment nécessaire pour assurer la durabilité de la ressource en eau souterraine dans ce pays.

La explotación de las aguas subterráneas para diferentes sectores en Camboya está en expansión. Los niveles de las aguas subterráneas ya han empezado a descender en algunas partes del país. El seguimiento y la evaluación de los cambios en el almacenamiento de las aguas subterráneas (GWS), el estrés del acuífero y la resiliencia del acuífero apoyarán la planificación y la gestión adecuadas de los recursos de aguas subterráneas del país; sin embargo, la información relativa a las aguas subterráneas en Camboya es actualmente escasa. Por lo tanto, se evaluó el cambio de GWS en Camboya durante los últimos 15 años, desde abril de 2002 hasta marzo de 2017, utilizando conjuntos de datos del Gravity Recovery and Climate Experiment (GRACE) y del Global Land Data Assimilation System (GLDAS) basados en la teledetección, con una validación exhaustiva de la anomalía de almacenamiento de aguas subterráneas (GWSA) derivada de GRACE con respecto a las observaciones in situ sobre el terreno. El presente estudio también investigó el impacto del cambio en el almacenamiento de agua superficial (SWS) en el lago Tonle Sap, el mayor lago de agua dulce del sudeste asiático, en la derivación del cambio del GWS en Camboya. También se evaluaron las tensiones de los acuíferos subterráneos (GAS) y la resistencia de los acuíferos (AR). Los resultados de la validación fueron promisorios, ya que el coeficiente de correlación entre las estimaciones basadas en satélites y las mediciones terrestres osciló entre 0.82 y 0.88 en cuatro subcuencas. La tasa global de disminución del GWS fue de ­0.63 mm/mes, con dos cuencas con la tasa de disminución más alta, de más de 1.4 mm/mes. Mientras tanto, el acuífero que experimentaba estrés durante la estación seca tenía una capacidad muy baja para recuperarse rápidamente de estas tensiones. Estos resultados ponen de relieve que se necesita urgentemente una gestión adecuada para garantizar la sostenibilidad del sistema de recursos hídricos subterráneos en este país.

A exploração de águas subterrâneas para diferentes setores no Camboja está se expandindo. Os níveis das águas subterrâneas já começaram a diminuir em algumas partes do país. O monitoramento e avaliação das mudanças no armazenamento de águas subterrâneas (AASub), estresse e resiliência do aquífero apoiarão o planejamento e a gestão adequados dos recursos hídricos subterrâneos do país; no entanto, as informações sobre as águas subterrâneas no Camboja são atualmente escassas. Assim, a mudança de AASub no Camboja nos últimos 15 anos, de abril de 2002 a março de 2017, foi avaliada usando conjuntos de dados Gravity Recovery and Climate Experiment (GRACE) e Global Land Data Assimilation System (GLDAS) baseados em sensoriamento remoto, com uma validação abrangente da anomalia de armazenamento de água subterrânea derivada do GRACE (AAASub) em relação a observações baseadas em campo. O estudo atual também investigou o impacto da mudança de armazenamento de água de superfície (AASup) no Lago Tonle Sap, o maior lago de água doce do Sudeste Asiático, na derivação da mudança de AASub no Camboja. Os estresses das águas subterrâneas no aquífero (SASub) e a resiliência do aquífero (RA) também foram avaliados. Os resultados da validação foram promissores, com o coeficiente de correlação entre as estimativas baseadas em satélite e as medições terrestres variando de 0.82 a 0.88 em quatro sub-bacias. A taxa global decrescente de AAS foi de ­0.63 mm/mês, com duas bacias tendo a maior taxa de declínio de mais de 1.4 mm/mês. Enquanto isso, o aquífero submetido a estresse durante a estação seca teve uma capacidade muito baixa de se recuperar rapidamente desses estresses. Esses achados enfatizam que uma gestão adequada é urgentemente necessária para garantir a sustentabilidade do sistema de recursos hídricos subterrâneos neste país.

A disaggregated assessment of national water security: An application to the river basins in Thailand.

Achieving water security is a global concern in the age of changing climate, population increase, urbanization, intensive socio-economic development, and land-use change. Addressing water security challenges is most appropriate at the river basin scale since hydrological boundaries at which water flows differ from administrative boundaries, and it can provide policymakers and decision-makers key insights to better support water management practices. This study carries out a disaggregated assessment of national water security by applying an indicator-based framework to evaluate water security conditions in all twenty-five river basins of Thailand from 2007 to 2015. The framework comprises five broad dimensions and eleven indicators. The study results revealed that the overall water security condition in Thai river basins has improved during this period. However, a fine-grained analysis at the dimensions and indicator level of water security shows that water productivity and the watershed health dimension are of concern in most river basins. The agricultural water productivity and the wastewater treatment capacity have deteriorated over the years in most basins. Likewise, it emerged that basins need to enhance their water resource management plans to account for future water challenges. The water security assessment framework presented in this study links well to the plans, policies, visions, and strategies developed for water resource management in Thailand. Thus, it can act as a decision-support tool to monitor the effectiveness of these plans and policies developed and arrive at interventions to enhance Thailand's water security.

A generalized methodology for ranking climate models based on climate indices for sector-specific studies: An application to the Mekong sub-basin.

This study proposes a methodological framework to evaluate and rank climate models based on extreme climate indices of precipitation and temperature for impact studies in seven sectors: Cryosphere, Energy, Forestry/GHGs, Health, Agriculture & Food Security, Disaster Risk Reduction (flood and drought), and Water Resources & Hydrology. The ranking of the climate models is based on their performance in sector-relevant extreme climate indices. Extreme climate indices for observed and climate models' datasets for a historical period and overall performance statistics were used to create a payoff matrix. The payoff matrix then served as an input to a multi-criteria decision-making process to rank the climate models for each of the climate indices. The final sector-specific ranking was achieved by averaging the ranks obtained in the sector-relevant indices. The developed methodology is demonstrated with an application to the Songkhram River Basin (Thailand), a sub-basin of the Mekong. Eighteen CMIP6 GCMs are used for the proposed evaluation and ranking processes and four performance statistics were used. Weights to each of the four performance statistics were determined using the entropy method. Compromise programming was applied to rank the GCMs based on the distance technique. The results indicate that the six best performing models are different for different sectors, with the GFDL_CM4 model common in all the seven sectors considered in the study. KACE1_0_G, GFDL_ESM4, GFDL_CM4, MRI_ESM2_0, and ACCESS_ESM1_5 models are the five top (ranked 1 to 5 respectively) performing models for the Water Resources & Hydrology sector. The developed framework is generic and can be applied to any region or basin; at the same time, it can also provide researchers and policymakers with specific information on best-performing models for particular sectors.

Measuring water security: A vital step for climate change adaptation.

Climate change and water are intricately linked. Water is the primary medium through which the impacts of climate change will be felt. Securing the water sector and enhancing water security is, therefore, imperative for any adaptive response to climate change. A precursor in improving water security is to first establish a mechanism to measure it. Only then can incremental and progressive actions be evaluated. This study has developed such a mechanism in the form of a water security assessment framework using an indictor-based methodology. The framework is developed for city-scale analysis because analyses at this scale is more useful in operationalizing water security enhancement. The framework has a three-layered structure comprising five dimensions (broad elements of water security), twelve indicators (areas of interest within the dimensions), and a set of potential variables that can be used to quantify the indicators. The framework has been developed to foster practical interventions for water security enhancement and not as a comparative tool for benchmarking. Hence, while the dimensions and indicators of the framework are fixed, the choice of variables is up to the city depending upon its context. This aspect of the framework, therefore, is meant to help cities introspect internally and move up the water security ladder. The framework culminates into a Water Security Index (WSI), measured on a scale from one to five. The scale is linear and hierarchical in its grade value. The framework was successfully used to assess the water security situation of Bangkok. The study also makes a case for scaling up this intervention for other major cities in Thailand, which can then help implement some of Thailand's key climate change adaptation initiatives such as the Nationally Determined Contributions and the National Climate Change Master Plan.

Evaluation of global land use/land cover products for hydrologic simulation in the Upper Yom River Basin, Thailand.

Recently, the availability of global landuse and land cover data has made hydrological simulation studies possible in data scarce regions. However, the suitability of these products as inputs in the hydrological modeling has not been investigated in detail. Therefore, this study aims to evaluate the use of global landuse and land cover products to simulate the hydrology of the Upper Yom River Basin located in the Northern part of Thailand. Three types of global landuse and landcover products i.e. ESACCI, MCD12Q1, GLC2000 were compared with the landuse product from Land Development Department (LDD) of Thailand. All of these products were used as input in hydrological model, Soil and Water Assessment Tool (SWAT), and performance of the model was compared to simulate hydrological regime including high flow, low flow and seasonal discharge at the outlet and upstream of the basin. The results show that the performance of the hydrological model in simulating the discharge at the basin outlet is better than in the upstream areas while using all types of landuse and land cover data. The model well simulated the annual discharge, wet-season discharge and base flow while using landuse and land cover products of ESACCI and MCD12Q1. Similarly, the high flow and dry-season discharge is well simulated while using MCD12Q1 landuse and landcover products compared to other three products. The results of this study is useful in selecting landuse and land cover products in simulating hydrology for water resources planning and management in data scarce regions.

Assessment of the impact of climate change and mining activities on streamflow and selected metal's loading in the Chindwin River, Myanmar.

The rapid expansion in mining activities is deteriorating the water quality in the Chindwin River of Myanmar. In addition, climate change may also aggravate this situation in future. Therefore, the aim of this study was to establish a connection between hydrology, mining area, heavy metal loading, and climate change in the Chindwin River. The hydrology of the upper Chindwin basin was modelled using SHETRAN hydrological model. Geochemical model PHREEQC was utilised to conduct speciation and saturation indexes modelling along the river in order to quantify the precipitated minerals along the river. Thereafter a regression relationship along with LOADEST model was used to quantify the heavy metal loads. Future climate was projected using four RCM's namely ACCESS1-CSIRO-CCAM, CCSM4-CSIRO-CCAM, CNRM-CM5-CSIRO-CCAM and MPI-ESM-LR-CSIRO-CCAM. Future discharges at water quality monitoring stations were simulated using the averaged ensembles. Finally, the heavy metal loading under future climate scenarios were analysed. Results indicate that climate change is likely to reduce future discharges by 3.4%-36.5% in all stations except in the Mokekalae station which shows 1.3%-9.4% increase in the near future discharges. Also, the projected metal loading under future climate conditions shows a decreasing pattern which is similar to the projected discharge pattern. In both baseline and future climate conditions, the area between stations Naung Po Aung and Uru downstream show the highest load effluent for both arsenic and mercury while the area between stations Uru downstream and Mokekalae show the highest load of iron effluent. Although future heavy metal loadings are expected to decrease, mining activities should be carefully monitored, since they discharge a large amount of toxic heavy metal loadings into the Chindwin River which is also expected to suffer a decrease streamflow in future.

Land use impact on the water quality of large tropical river: Mun River Basin, Thailand.

Globally, rivers and streams are experiencing declining water quality. Anthropogenic activities largely contribute to surface water pollution. Understanding human-induced influence on river water quality remains a challenge owing to spatiotemporal variations. In this study, we assessed the influence of various land uses (LU) on 16 water quality parameters of the Mun River, a tributary of the Mekong River, at different scales. Water quality was statistically analyzed both spatially and temporally (1995-2010). Seasonal and annual effect of LU on water quality was evaluated at buffer zone scale and sub-basin scale (i.e., catchment scale) using multiple regression analysis. The result showed that urban LU extensively adds to the nutrient concentration [i.e., total phosphorus (TP), ammonia nitrogen (NH3-N)] followed by agriculture LU at the sub-basin scale. Site-specific variability of TP is explained by urban LU and biological oxygen demand (BOD) by agriculture LU at the 5-km buffer in Upper and Middle Mun whereas at Lower Mun, the 20-km buffer explains the variability of suspended solids (SS) and total suspended solids (TSS), suggesting a more localized effect on the parameters upstream. The high concentration of parameters was noted in the dry season whereas the opposite was true for fecal coliform bacteria (FCB), SS, and TP. The maximum parameter concentration of NH3-N, FCB, and total coliform bacteria exceeds the permissible surface water quality standards of the Pollution Control Department (PCD) of Thailand in all three sub-basins. The study suggests the need for multi-scale interventions and effective pollution control measures focusing on nutrient, pathogenic bacteria, and solids pollution to improve the river water quality of large river basin.

Evaluation of climate change impacts and adaptation strategies on rainfed rice production in Songkhram River Basin, Thailand.

This study investigates rice yield and evaluates potential adaptation measures on field management practices for rainfed rice production under climate change scenarios in the Songkhram River Basin, Thailand. The top-down and bottom-up approaches are combined to evaluate the future climate conditions in the Songkhram River Basin and identify adaptation strategies respectively. An ensemble of four Regional Climate Models (RCMs) bias-corrected using the Quantile Mapping technique was used to project the future climate under two climate change scenarios (RCP4.5 and RCP8.5). The DSSAT crop simulation model was used to simulate rice yield and evaluate the impacts of climate change on rice yield, as well as the feasibility of four adaptation options, which were solicited from four hundred farmers through questionnaire surveys in the basin. The strategies include (i) change in planting date, (ii) change in fertiliser application date, (iii) change in fertiliser application dose, and (iv) supplying irrigation water. Based on the model results, future maximum and minimum temperatures are expected to increase by 2.8 and 3.2 °C respectively under RCP8.5 scenario for 2080s. Although annual rainfall may be unchanged, rainfall patterns will shift earlier in future. Evaluation of adaptation strategies suggest that supplying irrigation water under RCP4.5 and RCP8.5 scenarios respectively are the best strategies to increase rice yield under climate change scenarios. Change in fertiliser application date and change in planting date can increase the future rice yield by 12 and 8%, respectively under RCP4.5 scenario for 2080s. Adjusting the fertiliser application dose may however reduce future rice yield. Although supplying irrigation water can aid the production of rainfed rice, other concerns such as the source of water are involved. The feasibility of adaptation actions would depend largely on available resources and mindset of farmers. Further work is warranted in exploring a combination of adaptation strategies and management plans to combat the adverse impacts of climate change.

Quantifying the impact of climate change on crop yield and water footprint of rice in the Nam Oon Irrigation Project, Thailand.

Northeast Thailand makes a significant contribution to fragrant and high-quality rice consumed within Thailand and exported to other countries. The majority of rice is produced in rainfed conditions while irrigation water is supplied to rice growers in the dry season. This paper quantifies the potential impact of climate change on the water footprint of rice production using the DSSAT (CERES-Rice) crop growth model for the Nam Oon Irrigation Project located in Northeast Thailand. Crop phenology data was obtained from field experiments and used to set up and validate the CERES-Rice model. The present and future water footprint of rice, the amount of water evaporated during the growing period, was calculated under current and future climatic condition for the irrigation project area. The outputs of three regional climate models (ACCESS-CSIRO-CCAM, CNRM-CM5-CSIRO-CCAM, and MPI-ESM-LR-CSIRO-CCAM) for scenarios RCP 4.5 and RCP 8.5 were downscaled using quantile mapping method. Simulation results show a considerably high increase in the water footprint of KDML-105 and RD-6 rice varieties ranging from 56.5 to 92.2% and 27.5 to 29.7%. respectively for the future period under RCP 4.5, and 71.4 to 76.5% and 27.9 to 37.6%, respectively under RCP 8.5 relative to the simulated baseline water footprint for the period 1976-2005. Conversely, the ChaiNat-1 variety shows a decrease in projected water footprint of 42.1 to 39.4% under RCP 4.5 and 38.5 to 31.7% under RCP 8.5. The results also indicate a huge increase in the future blue water footprint, which will consequently cause a high increment in the irrigation water requirement in order to meet the plant's evaporation demand. The research outcome highlights the importance of proper adaptation strategies to reduce or maintain acceptable water footprints under future climate conditions.

Indicator-based approach for assessing the vulnerability of freshwater resources in the Bagmati River basin, Nepal.

To assess the vulnerability of water resources in the Bagmati River Basin in Nepal, this paper adopts an indicator-based approach wherein vulnerability is expressed as a function of water stress and adaptive capacity. Water stress encompasses indicators of water resources variation, scarcity, and exploitation and water pollution, whereas adaptive capacity covers indicators of natural, physical, human resource, and economic capacities. Based on the evaluation of eleven indicators, which were aggregated into eight vulnerability parameters, an increasingly stressful situation and lack of adaptive capacity became evident. Considerable spatial variation in indicator values suggests differential policy options. While the northern parts need attention to reduce pollution loading and conserve vegetation cover, the southern parts need improvements in physical capacity, i.e. water infrastructures. The comprehensive and easily interpretable findings of the study are expected to help decision makers reach sound solutions to reduce freshwater resources vulnerability in the Bagmati River Basin, Nepal. With its inherent flexibility, the approach has demonstrated its potential for application in different times and areas for monitoring and comparison purposes.