Public Health Implications of Drought in a Climate Change Context: A Critical Review.

Extreme weather events are expected to increase due to climate change, which could pose an additional burden of morbidity and mortality. In recent decades, drought severity has increased in several regions around the world, affecting health by increasing the risk of water-, food-, and vector-borne diseases, malnutrition, cardiovascular and respiratory illness, mental health disorders, and mortality. Drought frequency and severity are expected to worsen across large regions as a result of a decrease in precipitation and an increase in temperature and atmospheric evaporative demand, posing a pressing challenge for public health. Variation in impacts among countries and communities is due to multiple factors, such as aging, socioeconomic status, access to health care, and gender, affecting population resilience. Integrative proactive action plans focused on risk management are required, and resources should be transferred to developing countries to reduce their vulnerability and risk.

Analyzing the effects of drought at different time scales on cause-specific mortality in South Africa.

South Africa (SA) is highly vulnerable to the effects of drought on the environment, economy, and society. However, its effect on human health remains unclear. Understanding the mortality risk associated with different types of droughts in different population groups and by specific causes would help clarify the potential mechanisms involved. The study aims to comprehensively assess the effect of droughts of varying time scales on cause-specific mortality (all; infectious and parasitic; endocrine, nutritional, and metabolic; cardiovascular; respiratory) in SA (from 2009-2016) and identify more vulnerable profiles based on sex and age. We also evaluated the urbanicity and district-level socioeconomic deprivation as potential risk modifiers. We used a two-stage time-series study design, with the weekly standardized precipitation-evapotranspiration index (SPEI) calculated at 1, 6, 12, and 15 months of accumulation to identify droughts of different duration (SPEI1, 6, 12, 15, respectively). We applied a quasi-Poisson regression adjusted by mean temperature to assess the association between each type of drought and weekly mortality in all district municipalities of SA, and then pooled the estimates in a meta-regression model. We reported relative risks (RRs) for one unit increase of drought severity. Overall, we found a positive association between droughts (regardless the time scale) and all causes of death analyzed. The strongest associations were found for the drought events more prolonged (RR [95%CI]: 1.027 [1.018, 1.036] (SPEI1); 1.035 [1.021, 1.050] (SPEI6); 1.033 [1.008, 1.058] (SPEI12); 1.098 [1.068, 1.129] (SPEI15)) and respiratory mortality (RRs varied from 1.037 [1.021, 1.053] (SPEI1) to 1.189 [1.14, 1.241] (SPEI15)). An indication of greater vulnerability was found in younger adults for the shortest droughts, in older adults for medium-term and long-term droughts, and children for very long-term droughts. However, differences were not significant. Further evidence of the relevance of urbanicity and demographic and socioeconomic conditions as potential risk modifiers is needed.

Projected changes in atmospheric moisture transport contributions associated with climate warming in the North Atlantic.

Global warming and associated changes in atmospheric circulation patterns are expected to alter the hydrological cycle, including the intensity and position of moisture sources. This study presents predicted changes for the middle and end of the 21st century under the SSP5-8.5 scenario for two important extratropical moisture sources: the North Atlantic Ocean (NATL) and Mediterranean Sea (MED). Changes over the Iberian Peninsula-considered as a strategic moisture sink for its location-are also studied in detail. By the end of the century, moisture from the NATL will increase precipitation over eastern North America in winter and autumn and on the British Isles in winter. Moisture from the MED will increase precipitation over the southern and western portions of the Mediterranean continental area. Precipitation associated with the MED moisture source will decrease mainly over eastern Europe, while that associated with the NATL will decrease over western Europe and Africa. Precipitation recycling on the Iberian Peninsula will increase in all seasons except summer for mid-century. Climate change, as simulated by CESM2 thus modifies atmospheric moisture transport, affecting regional hydrological cycles.

Land-atmosphere feedbacks contribute to crop failure in global rainfed breadbaskets.

Global crop yields are highly dependent on climate variability, with the largest agricultural failures frequently occurring during extremely dry and hot years. Land-atmosphere feedbacks are thought to play a crucial role in agricultural productivity during such events: precipitation deficits cause soil desiccation, which reduces evaporation and enhances sensible heating from the land surface; the amplified local temperatures and moisture deficits can be detrimental to crop yield. While this impact of local land-atmosphere feedbacks on agricultural productivity has recently been reported, the dependency of crop yields on upwind regions remains understudied. Here, we determine the spatio-temporal origins of moisture and heat over the world's largest 75 rainfed breadbaskets, and illustrate the crop yield dependency on upwind regions. Further, we disentangle the role of local and upwind land-atmosphere interactions on anomalous moisture and heat transport during low-yield years. Our results indicate that crop failure increases on average by around 40% when both upwind and local land-atmosphere feedbacks cause anomalously low moisture and high heat transport into the breadbaskets. The impact of upwind land-atmosphere feedbacks on productivity deficits is the largest in water-limited regions, which show an increased dependency on moisture supply from upwind land areas. Better understanding these upwind-downwind dependencies in agricultural regions can help develop adaptation strategies to prevent food shortage in a changing climate.

Oceanic and terrestrial origin of precipitation over 50 major world river basins: Implications for the occurrence of drought.

The terrestrial and oceanic origins of precipitation over 50 major river basins worldwide were investigated for the period 1980-2018. For this purpose, we used a Lagrangian approximation that calculates the humidity that results in precipitation from the entire ocean area (ocean component of the precipitation, PLO) and the entire land area (land component, PLT) as well as the sum of both components (Lagrangian precipitation, PL). PL and its components were highly correlated with precipitation over the basins, where PLT accounted for >50 % of the PL in most of them. This confirmed the importance assigned by previous studies to terrestrial recycling of precipitation and moisture transport within the continents. However, the amount of PLO in almost all North American river basins was highlighted. The assessment of drought conditions through the Standardized Precipitation Index (SPI) at a temporal scale of 1- and 3-months revealed the number of drought episodes that affected each river basin, especially the Amazon, Congo, and Nile, because of the lower number of episodes but higher average severity and duration. A direct relationship between the severity of drought episodes and the respective severity computed on the oceanic and terrestrial SPI series was also found for the majority of basins. This highlights the influence of the severity of the SPI of oceanic origin for most basins in North America. However, for certain basins, we found an inverse relationship between the severity of drought and the associated severity according to the SPI of oceanic or terrestrial origin, thus highlighting the principal drought attribution. Additionally, a copula analysis provided new information that illustrates the estimated conditional probability of drought for each river basin in relation to the occurrence of drought conditions of oceanic or terrestrial origin, which revealed the possible main driver of drought severity in each river basin.

Uncertainty in surface wind speed projections over the Iberian Peninsula: CMIP6 GCMs versus a WRF-RCM.

This study assessed the projected near-surface wind speed (SWS) changes and variability over the Iberian Peninsula for the 21st century. Here, we compared Coupled Model Intercomparison Project Phase 6 global climate models (GCMs) with a higher spatial resolution regional climate model (RCM; ∼20 km), known as WRF-CESM2, which was created by a dynamic downscaling of the Community Earth System Model version 2 (CESM2) using the Weather Research and Forecasting (WRF) model. Our analysis found that the GCMs tended to overestimate observed SWS for 1985-2014, while the higher spatial resolution of the WRF-CESM2 did not improve the accuracy and underestimated the SWS magnitude. GCMs project a decline of SWS under high shared socioeconomic pathways (SSPs) greenhouse concentrations, such as SSP370 and SSP585, while an interdecadal oscillation appears in SSP126 and SSP245 for the end of the century. The WRF-CESM2 under SSP585 predicts the opposite increasing SWS. Our results suggest that 21st-century projections of SWS are uncertain even for regionalized products and should be taken with caution.

On the origin of the air between multiple tropopauses at midlatitudes.

Multiple tropopauses are structures that regularly recur in the midlatitudes. Recent studies have relied on the notion of the excursion of tropical air from the upper troposphere into higher latitudes, thereby overlaying the tropopause of the midlatitudes. We herein analyse the origin and characteristics of the air at the Boulder radiosonde station, between the first and second tropopauses combining an analysis of radiosonde data with a Lagrangian approach based on the FlexPart model and ERA-40 analysis data. Our results show that the air between both tropopauses has its origin in midlatitudes.

Dataset of outer tropical cyclone size from a radial wind profile.

Pérez-Alarcón et al. [1] developed a comparative climatology of the outer radius of tropical cyclones (TCs) from several radial wind profiles. They showed that the Willoughby et al. (2006) (W06) profile can be used to reproduce the TC tangential wind speed; thus, this profile is skilful for estimating the TC outer radius. Here, we present a database of TC sizes estimated from the W06 radial wind profile in each cyclogenetic basin worldwide. The database incorporates the critical wind radii, where the tangential wind speed is approximately 17.5 ms-1 (R34), 26 ms-1 (R50), 33 ms-1 (R64), and 51 ms-1 (R100), estimated by the W06 profile. The database has a comma-delimited text format with six-hour information on the location, maximum wind speed, central pressure, and the different TC metrics mentioned above. This database has a similar structure to that of the Atlantic Hurricane Database (HURDAT2) of the National Hurricane Center. The database presented here is applicable to studies on TC storm surge risks as well as to the determination of the sources and sinks of atmospheric moisture related to tropical cyclogenesis processes.

Oceanic versus terrestrial origin of El Niño Southern Oscillation-associated continental precipitation anomalies.

Precipitation is significantly influenced by the El Niño Southern Oscillation (ENSO), which is considered to be the most important factor that brings about climate variability. In this study, the asymmetry of the origin of continental precipitation anomalies during El Niño and La Niña events was investigated. An already validated Lagrangian approach was used to determine the proportion of the total Lagrangian precipitation that is of oceanic and terrestrial origin. Further, the role of these components of the Lagrangian precipitation in regions with significant precipitation anomalies during the ENSO was investigated. A two-phase asymmetric behavior of precipitation, particularly in tropical regions, was obtained. For some of these regions, precipitation anomalies based on other datasets were also calculated to confirm the observed changes, and for these regions, it was observed that in all cases, the calculated anomaly of Lagrangian precipitation agreed with the precipitation change. The percentage of precipitation of oceanic origin was higher in most of these regions. However, it was observed that an increase in the percentage of precipitation of oceanic origin did not bring about a general increase in precipitation for all the regions, revealing the importance of precipitation of terrestrial origin during both phases of the ENSO.

A data base of contributions of major oceanic and terrestrial moisture sources on continental daily extreme precipitation.

Most of the moisture transported in the globe has its origin in the well-known main moisture sources defined by Gimeno et al. [1]. They provide moisture for precipitation over continental areas in the world in different proportions. This paper presents the daily moisture contribution over each 0.5 × 0.5 continental gridded point from the three preferred moisture sources (primary, secondary, and tertiary) for continental extreme precipitation during the Peak Precipitation Month. The data consist of the moisture contribution ( | E - P < 0 | ) field by month from the three preferred sources obtained using an approach based on the Lagrangian particle dispersion model FLEXPART. The data here presented is directly related to the results presented in Vazquez et al. [2].

Effects of droughts on health: Diagnosis, repercussion, and adaptation in vulnerable regions under climate change. Challenges for future research.

There is little doubt about the effects of drought events on human health in the present climate. Projections of climate change indicate an increase in the occurrence and severity of droughts in the 21st century in a number of regions, thus it is likely that these types of hydrological extremes could have more of an impact if appropriate adaptation measures are not taken. The majority of studies on the effects of drought are focused on meteorological, agricultural, or hydrological contexts, but there are rather fewer assessments of the impacts of droughts on health. In particular, there have been hardly any attempts to compare different drought indices in order to identify and quantify the impacts of drought on health systems. In addition, rather better knowledge is needed on the mechanisms of vulnerability involved. In this paper, we attempt to describe the complexity of drought phenomena and the difficulty involved in quantifying the health risks linked to their occurrence. From an international perspective, we provide a brief review of the harmful effects of droughts on health in the context of climate change, as well as the vulnerability factors related to droughts. We make an assessment of aspects that have not yet been investigated, or which require further attention to be devoted to this topic. The principal aim of this paper is therefore to draw attention to the need to consider closely the relationship between drought indices and human health, in order to achieve a more fundamental understanding, and to propose specific courses or lines of action for future years, which could eventually be of use to healthcare providers and services.

Quantification of the Effects of Droughts on Daily Mortality in Spain at Different Timescales at Regional and National Levels: A Meta-Analysis.

A performance assessment of two different indices (the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI)) for monitoring short-term and short-medium-term drought impacts on daily specific-cause mortality in Spain was conducted. To achieve a comprehensive, nationwide view, a meta-analysis was performed using a combination of provincial relative risks (RRs). Moreover, the subdivisions of Spain based on administrative, climatic, and demographic criteria to obtain the measures of combined risks were also taken into account. The results of the SPEI and SPI calculated at the same timescale were similar. Both showed that longer drought events produced greater RR values, for respiratory mortality. However, at the local administrative level, Galicia, Castilla-y-Leon, and Extremadura showed the greatest risk of daily mortality associated with drought episodes, with Andalucía, País Vasco, and other communities being notably impacted. Based on climatic regionalization, Northwest, Central, and Southern Spain were the regions most affected by different drought conditions for all analyzed causes of daily mortality, while the Mediterranean coastal region was less affected. Demographically, the regions with the highest proportion of people aged 65 years of age and over reflected the greatest risk of daily natural, circulatory, and respiratory mortality associated with drought episodes.

Significant increase of global anomalous moisture uptake feeding landfalling Atmospheric Rivers.

One of the most robust signals of climate change is the relentless rise in global mean surface temperature, which is linked closely with the water-holding capacity of the atmosphere. A more humid atmosphere will lead to enhanced moisture transport due to, among other factors, an intensification of atmospheric rivers (ARs) activity, which are an important mechanism of moisture advection from subtropical to extra-tropical regions. Here we show an enhanced evapotranspiration rates in association with landfalling atmospheric river events. These anomalous moisture uptake (AMU) locations are identified on a global scale. The interannual variability of AMU displays a significant increase over the period 1980-2017, close to the Clausius-Clapeyron (CC) scaling, at 7 % per degree of surface temperature rise. These findings are consistent with an intensification of AR predicted by future projections. Our results also reveal generalized significant increases in AMU at the regional scale and an asymmetric supply of oceanic moisture, in which the maximum values are located over the region known as the Western Hemisphere Warm Pool (WHWP) centred on the Gulf of Mexico and the Caribbean Sea.

Changes in South American hydroclimate under projected Amazonian deforestation.

Continued deforestation in the Amazon forest can alter the subsurface/surface and atmospheric branches of the hydrologic cycle. The sign and magnitude of these changes depend on the complex interactions between the water, energy, and momentum budgets. To understand these changes, we use the weather research and forecasting (WRF) model with improved representation of groundwater dynamics and the added feature of Amazonian moisture tracers. The control simulation uses moderate resolution imaging spectroradiometer (MODIS) based observations of land use, and the deforestation simulations use a "business-as-usual" scenario projected for 2040-2050. Our results show that deforestation leads to changes that are seasonally very different. During the dry season, deforestation results in increased albedo and less available net radiation. This change, together with reduced leaf area, results in decreased evapotranspiration (ET), less atmospheric moisture of Amazonian origin, and an increase in temperature. However, we find no changes in precipitation over the basin. Conversely, during the wet season, surface winds increase significantly due to decreased surface roughness. Vapor transport increases throughout the deforested region and leads to an increase in easterly moisture export, and significant decrease in precipitation within the deforested regions of Eastern Amazon. Contrary to expectations, the moisture tracers in WRF show no evidence that precipitation decreases are due to recycling or changes in stability.

A database of optimal integration times for Lagrangian studies of atmospheric moisture sources and sinks.

Lagrangian methods for estimating sources and sinks of water vapour have increased in importance in recent years, with hundreds of publications over the past decade on this topic. Results derived from these approaches are, however, very sensitive to the integration time of the trajectories used in the analysis. The most widely used integration time is that derived from the average residence time of water vapour in the atmosphere, normally considered to be around 10 days. In this article, we propose an approach to estimate the optimal integration time for these Lagrangian methods for estimating sources and sinks, by comparing estimates of precipitation from the Lagrangian approach using different times of integration with results obtained from three state-of-the-art reanalyses, thereby providing a database of optimal integration times per month, for a spatial resolution of 0.25° × 0.25° in latitude and longitude.

An overview of offshore wind energy resources in Europe under present and future climate.

Long-term sustainable development of European offshore wind energy requires knowledge of the best places for installing offshore wind farms. To achieve this, a good knowledge of wind resources is needed, as well as knowledge of international, European, and national regulations regarding conflict management, marine environment conservation, biodiversity protection, licensing processes, and support regimes. Such a multidisciplinary approach could help to identify areas where wind resources are abundant and where conflicts with other interests are scarce, support measures are greater, and licensing processes are streamlined. An overview of offshore wind power studies at present, and of their future projections for the 21st century, allows for determining the optimal European locations to install or maintain offshore wind farms. Only northern Europe, the northwest portion of the Iberian Peninsula, the Gulf of Lyon, the Strait of Gibraltar, and the northwest coast of Turkey show no change or increase in wind power, revealing these locations as the most suitable for installing and maintaining offshore wind farms in the future. The installation of wind farms is subject to restrictions established under international law, European law, and the domestic legal framework of each EU member state. Europe is moving toward streamlining of licensing procedures, reducing subsidies, and implementing auction systems.

From Amazonia to southern Africa: atmospheric moisture transport through low-level jets and atmospheric rivers.

A Lagrangian analysis is applied to identify the main moisture source areas associated with atmospheric rivers (ARs) making landfall along the west coast of South Africa during the extended austral winter months from 1980 to 2014. The results show that areas that provide the anomalous uptake of moisture can be categorized into four regions: (1) the South Atlantic Ocean between 10°S and 30°S, (2) a clear local maximum in the eastern South Atlantic, (3) a continental source of anomalous uptake to the north of the Western Cape, and (4) over South America at a distance of more than 7000 km from the target region. It emerges that the South American moisture source can be linked to a particular phase of the South American low-level jet, known as a no Chaco jet event (NCJE), which transports moisture to the western and central South Atlantic basin. Concisely, we provide strong evidence that the two margins of the South Atlantic Ocean appear connected by two meteorological structures, with the NCJE playing a key role of transporting moisture from South America to the western and central South Atlantic basin, feeding the AR that transports some of the moisture to the west coast of South Africa.

Rapid termination of the African Humid Period triggered by northern high-latitude cooling.

The rapidity and synchrony of the African Humid Period (AHP) termination at around 5.5 ka are debated, and it is unclear what caused a rapid hydroclimate response. Here we analysed the hydrogen isotopic composition of sedimentary leaf-waxes (δDwax) from the Gulf of Guinea, a proxy for regional precipitation in Cameroon and the central Sahel-Sahara. Our record indicates high precipitation during the AHP followed by a rapid decrease at 5.8-4.8 ka. The similarity with a δDwax record from northern East Africa suggests a large-scale atmospheric mechanism. We show that northern high- and mid-latitude cooling weakened the Tropical Easterly Jet and, through feedbacks, strengthened the African Easterly Jet. The associated decrease in precipitation triggered the AHP termination and combined with biogeophysical feedbacks to result in aridification. Our findings suggest that extratropical temperature changes, albeit smaller than during the glacial and deglacial, were important in triggering rapid African aridification during the Holocene.

Atmospheric transport towards the Iberian Peninsula in the 3- to 10-day range.

An advanced Lagrangian atmospheric transport model (FLEXTRAP) was used to identify the possible sources of middle-lived pollutants over the Iberian Peninsula. A period of 4 years, 2000-2003, was analyzed. Transatlantic transport is the main pathway of the air reaching the Iberian Peninsula in the studied range of 3-10 days; local sources are limited to 3 days of transport. The presence of North America as a source from days 6-10 of transport identifies this region as the main potential contributor to the middle-lived pollutants over the Iberian Peninsula.