Implications of climate change and drought on water requirements in a semi-mountainous region of the Vietnamese Mekong Delta.

As the backbone of Vietnam's economy, the country has recently established a number of policies for promoting and investing in smart agriculture in the Mekong Delta, the country's largest agricultural hub, to foster overall socio-economic development. However, water remains a critical constraint for crop production, with progress being hindered by water scarcity and quality issues, and compounded by socio-economic transformation and climate change. Considering these challenges, this study used the CROPWAT model and a wide spectrum of climate change scenarios to investigate future total water demands in the 2030s and 2050s as well as drought levels in two underdeveloped semi-mountainous reservoir catchments, i.e., O Ta Soc and O Tuk Sa in An Giang province. The results suggest that the usable storage capacity of the O Ta Soc reservoir will increase to 650,000 m3 to meet water supply demands under all climate change scenarios and the medium-term, moderate drought conditions. The useable storage capacity of the O Tuk Sa reservoir will also be increased to 880,000 m3 and the irrigation area would see a marked 70% reduction compared to its design irrigation. Under these circumstances, the O Tuk Sa reservoir will continue to supply water under all climate change scenarios and medium-term droughts. As a core element for strategic planning and to ensure efficient management of water resources, the results highlight the importance of estimating potential runoff and rainfall in semi-mountainous reservoir catchments under various drought conditions in order to propose the suitable expansion of the useable water storage capacities.

Modified version for SPEI to evaluate and modeling the agricultural drought severity.

Drought is a climatic phenomenon that can occur in various regions with different climate conditions. Generally, drought has negative impacts on different fields such as environment, rangelands, and water resources. The agricultural section (especially rain-fed agriculture) is one of the parts that is directly affected by different types of drought especially meteorological and agricultural droughts. The standardized precipitation evapotranspiration index (SPEI) is one of the newest and most applied indices to assess drought characteristics. In this paper, a modification is suggested for SPEI with the substitution of observed precipitation (OP) with effective precipitation (EP) to evaluate drought, with an emphasis on consideration of drought effects on agricultural section. To calculate EP, Food and Agriculture Organization of the united nation method (FAO), US Bureau of Reclamation (USBR), the Simplified version of Soil Conservation Service of the US Department of Agriculture method (USDA-SCS simplified), and the CROPWAT version of USDA-SCS method (USDA-SCS CROPWAT) were used. To compare the calculated SPEI based on OP (SPEIOP) and EP (SPEIEP) (based on different EP calculation methods), the correlation coefficients (CC) between SPEIOP and SPEIEP in four synoptic stations with at least 30 years of climatic data and annual yield loss (%) in winter wheat (Triticum sativum) (simulated using AquaCrop model) in the suitable reference periods for agricultural drought were used. Results showed, in Fasa, Drodzan, and Zarghan stations, the CC between SPEI based on EP using the USBR method (SPEIUSBR) and annual YL% had the highest values (in 42.11%, 68.42%, and 36.84% of Triticum sativum all reference periods, respectively). In Shiraz station, the CC between SPEI based on EP using the FAO method (SPEIFAO) and annual YL% had the highest values (in 47.37% of all reference periods). In all stations, the SPEIUSBR had the most reference periods with significant CC at 0.05 or 0.01 levels.

Increase in economic efficiency of water use caused by crop structure adjustment in arid areas.

The Heihe River is located in the arid zone of northwestern China. In its middle-reach region, irrigation agriculture is well developed. With rapid population growth and expansion of the cultivated land in this region, effective water resource use is vital for the sustainable development of the river basin and the increase of incomes from farming practices. In this study, based on farmer survey data, the input parameters of the CROPWAT model were modified, the water use amount was simulated after deducting the influences of climate, seeds, and irrigation systems, and the variation of economic efficiency of water use (EEWU) induced by crop structure adjustment from 2001 to 2012 was analyzed. The results show that simulations for evapotranspiration of maize based on the CROPWAT model are in accord with the observed data. From 2001 to 2012, due to changes in the regional crop structure, EEWU in the study area increased by about 40%. In the arid areas in northwest China, crop structure adjustment has a huge potential for improving EEWU and increasing incomes from farming practices.

Crop water requirement and irrigation scheduling under climate change scenario, and optimal cropland allocation in lower kulfo catchment.

Crop water requirement and irrigation scheduling in Lower Kulfo Catchment of southern Ethiopia have not assessed under climate change scenarios, and the allocation of crop land also not optimal that signifcantly challenges to crop productivity.Therefore, this study was conducted to evaluate the effects of climate change on future crop water requirements, and irrigation scheduling, and to allocate cropland optimally. Bias of projected precipitation and temperature were corrected by utilizing Climate Model data with the hydrologic modeling tool (CMhyd). Alongside, crop water requirements and irrigation scheduling were assessed using Crop Water Assessment Tool. After estimating crop water requirement, crop land were allocated optimally using General Algebraic Modeling System programming with non-negativity constraints (scenario 1), and non-negativity constraints based on farmers adaptation (scenario 2). Average reference evapotranspiration from 2030 to 2050 and 2060 to 2080 was increased by 11.9 %, and 16.2 %, respectively compared with the reference period (2010-2022). The total seasonal crop water requirements were 4,529 mm, 4866.7 mm, and 5272.2 mm under 2010 to 2022, 2030 to 2050, and 2060 to 2080 climate change scenarios, respectively. The meean irrigation interval in 2010-2022, 2030 to 2050, and 2060 to 2080 climate change scenarios were 8 days, 7 days, and 5 days, respectively. This irrigation interval was decreased by 14 % (2030-2050), and 34 % (2060-2080) compared with the reference period. In 2030 to 2050 and 2026 to 2080 climate change scenarios, the required irrigation water at the inlet of main canal increased by 6.8 %, and 18 %, respectively. The optimal allocated area for tomato (60.4 %), maize (20.8 %), and watermelon (18.8 %) in scenario 1 with net benefit of 1.47*108 Ethiopian Birr. The allocated areas in scenario 2 were (48 %) for maize, (31.6 %) for tomato, and (20.4 %) for watermelon with 1.34*108 Ethiopian Birr net benefit it was reduced by 19.1 % compared with the net benefit in scenario 1. Fruit crops alone may not suffice for local food needs and to address this, small farmers should grow maize, tomato, and watermelon. This research aids policymakers in encouraging climate-resilient agriculture and improving small-scale farmers' awareness through conducting workshops and training.

Impact of climate change on shumbrite small scale irrigation project, South Gojjam subbasin, Ethiopia.

Climate change has the potential to affect climate parameters like rainfall and temperature which lead to a change in the irrigation water requirement of the irrigation system. As irrigation water requirement is highly dependent on precipitation and potential evapotranspiration, climate change impact studies are necessary. Therefore, this study aims to assess the impact of climate change on the irrigation water requirement of the Shumbrite irrigation project. For this study, climate variables of precipitation and temperature were generated from CORDEX-Africa simulations downscaled from MPI Global Circulation Model (GCM) under three emission scenarios (RCP2.6, RCP4.5, and RCP8.5). The climate data covers from 1981 to 2005 for the baseline period and 2021-2045 for the future period for all scenarios. Future precipitation shows a decrease for all scenarios with a maximum decrease under RCP2.6 (4.2%) and temperature show an increase in the future as compared to the baseline period. The reference evapotranspiration and Irrigation Water Requirements (IWR) were calculated by using CROPWAT 8.0 software. Results showed that the mean annual reference evapotranspiration is expected to increase in the future by 2.7%, 2.6%, and 3.3% for RCP2.6, RCP4.5, and RCP8.5 respectively as compared to the baseline period. Mean annual irrigation water requirement shows an increase of 2.58%, 0.74%, and 8.4% for the future under RCP2.6, RCP4.5, and RCP8.5 respectively. The Crop Water Requirement (CWR) also increases for the future period under all RCP scenarios, with maximum CWR for tomato, potato, and pepper crops. To ensure the sustainability of the project, crops with high irrigation water requirements should be replaced by other crops with low water requirements.

Performance analyses of effective rainfall estimation methods for accurate quantification of agricultural water footprint.

Water footprint (WF) assessments have become a significant tool for the sustainable management in recent years. Effective rainfall (Peff) is a critical indicator for characterizing soil moisture (green water, WFgreen) and calculating irrigation requirements (blue water, WFblue). However, majority of the water footprint analyses employ empirical or numerical models to predict Peff, and the number of studies for experimental validation of these models are quite insufficient. The main scope of this study is to test the performance of commonly used Peff estimation models in relation to the soil water balance (SWB) of an experimental site. Accordingly, the daily and monthly soil water budget is estimated from a maize field which is characterized as semi-arid land with continental climate (Ankara, Turkey), equipped with moisture sensors. Then, Peff, WFgreen, and WFblue parameters are calculated using FP, US-BR, USDA-SCS, FAO/AGLW, CROPWAT, and SuET methods and compared with SWB method. Employed models were highly variable. CROPWAT and US-BR predictions were the most accurate. In majority of months, the CROPWAT method estimated the Peff with a maximum deviation of 5% from the SWB method. In addition, the CROPWAT method predicted blue WF with an error less than 1%. The widely utilized USDA-SCS approach did not produce expected results. The FAO-AGLW method provided the lowest performance for each parameter. We also find that the errors in estimating Peff in semi-arid conditions cause green and blue WF outputs to be quite less accurate than the dry and humid cases. This study provides one of the most detailed assessments about the impact of effective rainfall on the blue and green WF results with high temporal resolution. The findings of this study are important for the accuracy and performance of the formulae used in Peff estimations and to develop more precise blue and green WF analyses in the future.

Green water appropriation of the cropland ecosystem in China.

Despite the awareness that green water is the main source of water to produce food, studies on green water use in cropland ecosystems are still rather limited, and almost no research has so far explored the relationship between green water utilization and socioeconomic development. In this study, with the help of CropWat 8.0, the green water footprint (GWF) of main crops in China was estimated from 1979 to 2016. On this basis, a novel concept, i.e., green water appropriation rate (GWar), was introduced to reveal the relationship between GWF and precipitation. Then, for the first time, the center of gravity trajectory of the GWar and the correlation between GWar and socioeconomic factors were further investigated. The results show that the provinces with the largest increases of GWF were Inner Mongolia (223%), Xinjiang (127%), and Ningxia (123%), while the GWF of 11 provinces has decreased, and 9 of them were municipalities or coastal areas. Generally, the GWar in the eastern and central provinces was higher than that in the western provinces. The center of gravity of the GWar has always been in Henan Province, but it has moved westward from Kaifeng City in 1979 to Sanmenxia City in 2016 and may further move to Shanxi Province soon. The total power of agricultural machinery and the effective irrigation rate had a positive correlation with the GWar, while the agricultural GDP was negatively correlated with the GWar. It is expected that the results will explicitly provide a scientific basis for the development of water-appropriate agriculture and the full utilization of rainwater.

Quantification of water requirement of some major crops under semi-arid climate in Turkey.

The Southeastern Anatolian Region of Turkey is located in semi arid climate zone and therefore requires an efficient water use. Well-planned irrigation with optimum water required by the crops is essential for the limited water resources of the region. The numerical tool CROPWAT of the Food and Agriculture Organization (FAO) was used for modelling efficient irrigation of local crops pistachio, olive, almond and grape without reducing the yield. Local climatic, soil, plant and rainfall information were used as inputs to CROPWAT model to predict the reference evapotranspiration (ETo) values. The crop water requirement (CWR) for pistachio, olive, almond, and grape was calculated as 1,294.0 mm, 659.4 mm, 790.2 mm, and 752.0 mm, respectively, The number of irrigation needed during growth stages was determined as eight for pistachio, three for olive, six for almond and five for grape.

The water footprint of irrigation-supplemented cotton and mung-bean crops in Northern Ethiopia.

Global freshwater resources are getting scarcer and scarcer due to the ever-increasing population, climate change, and other human activities. Hence, assessing the consumption of freshwater by different consumers is a key to efficiently utilize the resource. In this study, the Water Footprint Assessment (WFA) tool was used to determine the water footprint (WF) of Center Pivot (CP) irrigated cotton and mung-bean production using two approaches, namely, CROPWAT and field-data based methods. Based on the CROPWAT-based estimates, the average total WF of cotton was found to be 2745 m3/ton. Out of this, the green and blue WF contributed to an average of 35% and 65 %, respectively. For mung-bean, the total WF was 6561m3/ton, of which blue WF covered around 93 %. Comparison of the blue WF from CROPWAT and field-data based estimates showed a good agreement (nRMSE = 4.5 %, nMBE = 10.7 % and relative error/RE/ranging from 0.8 to 17% for cotton and 12.6% for mung-bean) and no significant difference (p = 0.456) was obtained between the two estimates. The effect of planting date on the WF estimation also showed a small variation of 0.7%-6.6 % for cotton and up to 12% for mung-bean. However, major reductions were obtained on the blue WF of cotton and mung-bean as a result of changing planting dates by about two months prior to the baseline planting dates. In this study, it is concluded that WF assessment could be satisfactorily estimated using CROPWAT model if supported with field obtained information such as soil, crop, and weather data. Another finding of the present study was that, changing planting dates close to the major rainy months could substantially contribute to reducing the blue WF in similar climates.