Drought-vulnerable Regions Research Articles

Probabilistic assessment of vegetation vulnerability to drought stress in Central Asia

The increasing frequency and intensity of droughts in a warming climate are likely to exacerbate adverse impacts on ecosystems, especially for water-limited regions such as Central Asia. A quantitative understanding of the impacts of drought on vegetation is required for drought preparedness and mitigation. Using the Global Inventory Modeling and Mapping Studies NDVI3g data and Standardized Precipitation Evapotranspiration Index (SPEI) from 1982 to 2015, we evaluate the vegetation vulnerability to drought in Central Asia based on a copula-based probabilistic framework and identify the critical regions and periods. Furthermore, a boosted regression trees (BRT) model was also used to explore the relative importance of environmental factors and plant traits on vegetation response to drought. Additionally, we also investigated to what extent irrigation could alleviate the impacts of drought. Results revealed that months from June to September was the critical period when vegetated areas were most vulnerable to drought stress. The probabilities of vegetation loss below 20th quantile under extremely dry in these months were 68.7%, 69.4%, 71.0%, and 67.0%, respectively. Regarding vegetation-vulnerable regions, they shifted with different growth stages. During the middle of the growing season, semi-arid areas were the most vulnerable regions, whereas the highest drought-vulnerable regions were observed in arid areas during other periods. The BRT results showed that plant traits accounted for a large fraction (58.9%) of vegetation response to drought, which was more important than ambient soil environment (20.8%). The analysis also showed that mitigations from irrigation during July to September were smaller than in other months. The results of this paper provide insight into the influences of drought on vegetation and may contribute to drought mitigation and land degradation measures in Central Asia under accelerating global warming.

Addition of Criteria for the Drought Level Vulnerability to the Reservoir Location Priority

Blora regency is mostly a water critical region during dry seasons due to its porous soil characteristic. In order to overcome this condition, in 2006, Indonesian Ministry of Public Works and Housing, through Mettana Engineering Consultant, conducted a Study of Identification and Basic Design Development of Reservoirs in Blora Regency. It determined 28 future reservoir locations by considering their technical, economical and socio-environmental aspects. However, for the reservoirs to be the most effective, it is necessary to include regional drought vulnerability aspect into consideration to determine their location priority. The main purpose of this research, to conduct an analysis of meteorogical drought vulnerability in Blora regency region.In more detail the main goal is to determine reservoir location priority in Blora regency region by considering meteorogical drought vulnerability aspect. Drought Index was calculated using SPI (Standardized Precipitation Index ) method using 2009-2018 monthly precipitation data obtained from 15 precipation stations. Mapping of drought vulnerable regions was done using GIS (Geographic Information System) technology using spatial interpolation approach. This research determined new priority, different from that determined by Mettana Engineering Consultant. Priority 1 formerly consisted of Suruhan, Kedungwungu, Bangsri, Sambong and Kalisari reservoirs while the new one consisted of Polaman 1, Polaman 2, Suruhan and Jurangjero reservoirs. Suruhan reservoir appeared in both versions. Kedungwungu, Bangsri, Sambong and Kalisari reservoirs moved to priority 2 in the new priority since they were located in low drought level regions while Polaman 1, Polaman 2 and Jurangjero reservoirs moved to priority 1 since they were located in moderately high to moderate drought level regions. It indicated that is necessary to include drought vulnerability aspect into consideration in determining reservoir location, along with technical, economical and socio-enviromental aspects. The government then may employ this aspect as an additional criteria in developing future reservoir construction program to be more effective that targets drought vulnerable regions

Bivariate probabilistic quantification of drought impacts on terrestrial vegetation dynamics in mainland China

Frequent droughts in a warming climate may exert more negative influences on ecosystems. Unlike previous studies that have investigated the vegetation response to drought generally in a deterministic way, a copula-based model is developed for quantifying drought impacts on terrestrial vegetation and identifying drought-vulnerable regions for mainland China from a probabilistic perspective in this study. The Normalized Difference Vegetation Index (NDVI) is firstly correlated with the Standardized Precipitation Evapotranspiration Index (SPEI) at varying timescales from 1 month to 24 months to determine the response time of vegetation to water variability. Then, the dependence structure of vegetation vigor and water availability is modeled through the bivariate copula analysis. Furthermore, conditional probabilities of vegetation decline under moderate, severe and extreme drought scenarios are systematically estimated using copula-based conditional probability distributions. Results indicate that spatial patterns of vegetation response time present distinct seasonality, with faster response to water variation in the southern part than in the northern proportion of mainland China during the non-growing season while the inverse pattern is observed for the growing season. The higher conditional probabilities of the below-average vegetation status in the dry condition evidence that water deficits overwhelming water surplus play a more profound role in diminishing vegetation vigor across more than 80% of mainland China. Specifically, when moderate droughts develop into extreme ones, the average probability of vegetation status below the 50th percentile escalates by 6.9%. Moreover, extreme droughts are noted to exaggerate probabilities of vegetation activity falling below the increasingly lower (40th, 30th, 20th and 10th) percentiles by 8.8%, 10.8%, 12.7% and 13.7% in comparison with moderate counterparts, thereby suggesting higher likelihood of the deteriorating drought conditions inducing vegetation losses, especially major vegetation decline. As for the drought-vulnerable region, North China, particularly the central Inner Mongolia, is recognized with vegetation decline probabilities being 28.1% and 68.8% greater than the mainland average given drought conditions (quantified as SPEI ≤ −1), respectively. Results of the study may improve our understanding of climatic extreme influence on vegetation status and benefit the effective drought preparedness and mitigation.

Probabilistic assessment of remote sensing-based terrestrial vegetation vulnerability to drought stress of the Loess Plateau in China

Quantitative understanding of vegetation vulnerability under drought stress is essential to initiating drought preparedness and mitigation. In this study, a bivariate probabilistic framework is developed for assessing vegetation vulnerability and mapping drought-prone ecosystems more informatively, which is different from previous studies conducted in a deterministic way. The Normalized Difference Vegetation Index (NDVI) is initially correlated to the Standardized Precipitation Index (SPI) at contrasting timescales to evaluate the degree of vegetation dependence on water availability and screen out the vegetation response time. Afterward, the monthly NDVI series is connected with the most correlated SPI to derive joint distributions using a copula method. On such basis, conditional probabilities of vegetation losses are estimated under multiple drought scenarios and used for revealing tempo-spatial patterns of vegetation vulnerability. Particular focus is directed to the Loess Plateau (LP), China, which is a world-famous environmentally fragile area. Results indicate that the proposed framework is valid for vegetation vulnerability assessment as the pair-wise SPI-NDVI observations fall within high-density areas of the estimated NDVI distributions. From a probabilistic perspective, roughly 95% of the LP exhibits greater probability of vegetation losses when suffering from water deficits rather than water surplus. Vegetation loss probabilities reaching their peak (39.7%) in summer indicate the highest vegetation vulnerability to drought stress in summer months sequentially followed by autumn (32.9%) and spring (31.0%), which is linked to marked variations in water requirement at different stages of vegetation growth. Spatially, drought-vulnerable regions are identified in the western edge with vegetation loss probability 20.6% higher than the LP mean value, suggesting higher vulnerability in more arid areas. Irrigation practices and large-scale vegetation restoration, as two important sources of anthropogenic disturbance in the LP, benefit the decreased vegetation vulnerability over the majority of affected areas. Results may increase our knowledge about climatic controls on vegetation health and support the ecosystem restoration planning in the LP.

Multi-scale assessment of eco-hydrological resilience to drought in China over the last three decades

Understanding to what extent can terrestrial ecosystems maintain their structure and functions and recover after being hit by drought is critical for sustainable ecosystem management and drought mitigation practices. This study assesses multi-scale (i.e., at grid, climate type, land use, basin, province scales) eco-hydrological resilience to drought over China during the period of 1982–2015, based on Standard Evapotranspiration Deficit Index as well as satellite-retrieved evapotranspiration (ET) and net primary production (NPP). Over the last three decades, the ecosystem water use efficiency (eWUE) increased in most regions of China (especially in Northeast China and North China Plain) in the context of climate change. The western China showed a significant wetting trend with ascending ET, GPP and eWUE. The SEDI and ET showed significantly increasing tendencies but the ecosystem GPP and eWUE did not exhibit obvious responses to regional wetting in the middle and lower reaches of Yangtze River basin. Most terrestrial ecosystems in China were found overall resilient to drought except for mild temperature-fully humid-warm summer at the climate type scale, water type at the land use scale, Northwest Rivers at the basin scale as well as Ningxia, Qinghai, Shanghai and Hong Kong at the province scale. These findings would facilitate the identification of most drought-vulnerable regions for ecosystem management and taking reasonable adaptation measures (e.g., use of alternative water resources or reuse water, water conservation and smart irrigation) to ensure the sustainability of terrestrial ecosystems during the drought periods over China.

Assessing the vulnerability of farm families towards drought in Kermanshah province, Iran

Drought as a natural disaster and an inevitable phenomenon has impacted different countries such as Iran. Since most Iranian rural households are dependent on agricultural production, they are severely vulnerable to drought. Studies on drought vulnerability have focused on individual farmers with less attention to the farm families. Therefore, the purpose of this survey research was to determine the vulnerability of farm families in Droud Faraman region, Kermanshah. The population comprised of 3329 households in which 172 farm families were selected using multi-stage random sampling techniques. Drought vulnerability was assessed using Deressa et al. formula that measures adaptive capacity, exposure and sensitivity. Results revealed that farm families formed three clusters of vulnerability, i.e. low, moderate and high drought vulnerability. Moreover, Kahrar Moghoofe and Choobderaz villagers were most vulnerable towards drought whereas Moradabad and Amme villagers were least vulnerable to this phenomenon. This study has implications for drought mitigation programs in Kermanshah province. Limited resources should focus on drought vulnerable regions so that adaptive capacities in those regions would be enhanced.

Exploring evapotranspiration dynamics over Sub-Sahara Africa (2000-2014).

Monitoring changes in evapotranspiration (ET) is useful in the management of water resources in irrigated agricultural landscapes and in the assessment of crop stress and vegetation conditions of drought-vulnerable regions. Information on the impacts of climate variability on ET dynamics is profitable in developing water management adaptation strategies. Such impacts, however, are generally unreported and not conclusively determined in some regions. In this study, changes in MODIS (Moderate Resolution Imaging Spectroradiometer)-derived ET (2000-2014) over large proportions of Sub-Sahara Africa (SSA) are explored. The multivariate analyses of ET over SSA showed that four leading modes of observed dynamics in ET, accounting for about 90% of the total variability, emanated mostly from some sections of the Sudano-Sahel and Congo basin. Based on Man-Kendall's statistics, significant positive trends (α = 0.05) in ET over the Central African Republic and most parts of the Sahel region were observed. Over much of the Congo basin nonetheless, ET showed significant (α = 0.05) distributions of widespread negative trends. These trends in ET were rather found to be consistent with observed changes in model soil moisture but not in all locations, perhaps due to inconsistent trends in maximum rainfall and land surface temperature. However, the results of spatio-temporal drought analysis confirm that the extensive ET losses in the Congo basin were somewhat induced by soil moisture deficits. Amidst other prominent drivers of ET, the dynamics of ET over the terrestrial ecosystems of SSA appear to be a more complex phenomenon that may transcend natural climate variations.

Spatio-temporal drought risk mapping approach and its application in the drought-prone region of south-east Queensland, Australia

Strategic management of water resources in drought-vulnerable regions can be greatly hampered by frequent, severe and long-lasting droughts. To enable better drought relief policy and amicable solutions and proactive actions for preparedness and mitigation of drought impacts, this study adopts a spatio-temporal methodology for the assessment of drought risk of drought-prone areas in south-east Queensland, Australia. In this study, the spatially representative depiction of the drought risk in a drought-prone region with multiple vulnerability, exposure and drought hazard indicators is considered in order to develop a geographic information systems-based drought risk mapping tool. Spatial indicators of drought are categorised into various subclasses, and the conditional joint probability of each indicator is the determined in accordance with the Bayes theorem. The fuzzy logic approach is then embraced as a new approach in this study to standardise the different drought factors on a range of 0–1 followed by an aggregation of drought vulnerability, exposure and hazard indices using the fuzzy GAMMA overlay operation in ArcGIS 10.5 to produce the optimal drought risk map for the case study region. The analysis of drought’s different phases shows varying vulnerability levels in different austral seasons (summer, autumn and spring of 2007) and annually (2007, 2009 and 2013) that is well represented by drought hazard index, i.e. rainfall departure. The application of the fuzzy set to incorporate and classify drought factors reveals its useful implications for handling of spatial drought-related data and the development of the drought risk index. The validation of the method performed with upper and lower layer soil moisture data reveals significant correlation with the drought risk index. The study has implications for drought risk mapping, particularly in utilising the ability of the fuzzy logic-based analytical technique integrated with GIS-based mapping tools for spatio-temporal drought risk studies. The approach in this paper can be considered as a practical mapping tool for drought studies, to better enable drought management, drought mitigation and relief-planning actions that need to be implemented by different decision-makers in water resources, agriculture and other socio-economic areas.

Investigation of drought-vulnerable regions in North Korea using remote sensing and cloud computing climate data.

Drought is one of the most severe natural disasters in the world and leads to serious challenges that affect both the natural environment and human societies. North Korea (NK) has frequently suffered from severe and prolonged droughts since the second half of the twentieth century. These droughts affect the growing conditions of agricultural crops, which have led to food shortages in NK. However, it is not easy to obtain ground data because NK is one of the most closed-off societies in the world. In this situation, remote sensing (RS) techniques and cloud computing climate data (CCCD) can be used for drought monitoring in NK. RS-derived drought indices and CCCD were used to determine the drought-vulnerable regions in the spring season in NK. After the results were compared and discussed, the following conclusions were derived: (1) 10.0% of the total area of NK is estimated to be a drought-vulnerable region. The most susceptible regions to drought appear in the eastern and western coastal regions, far from BaekDu-DaeGan (BDDG), while fewer drought regions are found near BDDG and the Nahngrim Mountains. The drought-vulnerable regions are the coastal regions of South Hamgyong Province, North Hamgyong Province, South Pyongan Province, and South Hwanghae Province. The latter region is the food basket of NK. (2) In terms of land cover, the drought-vulnerable regions mainly consisted of croplands and mixed forest.

Long-term spatio-temporal drought variability in Turkey

The spatio-temporal variability of drought is presented by evaluating homogeneously distributed 250 station records from 1931 to 2010 for 80years’ duration in Turkey. The drought analysis is implemented using Standardized Precipitation Index (SPI) in terms of SPI-1, SPI-3, SPI-6, SPI-6AS (SPI-6 April to September) and SPI-12. The principle component analysis (PCA) is applied to SPI time series to identify spatial and temporal drought patterns. SPI time series are classified into two groups (1st group: SPI-1, SPI-3, SPI-6AS; and 2nd group: SPI-6 and SPI-12) according to the similarity in spatial drought patterns. SPI-3 and SPI-12 are selected as representative members of each group for spatio-temporal analysis. A relationship among correlation area (An), correlation coefficient (CC), principle component numbers (Fn) and total variances explained (Vexp) are investigated for identifying four well-defined drought vulnerable homogeneous regions over Turkey mainland. Mean percentages of extreme, severe, and moderate drought areas are calculated as 3.13% (2.81%), 3.75% (4.06%) and 7.19% (7.50%) for SPI-3 (SPI-12) based on 80years in all drought vulnerable regions. Spectral characteristics of drought are also investigated based on fast Fourier transform (FFT) method. It is observed that while southeastern and western parts of Turkey are more stable due to the highly-correlated variances of spatial patterns; central parts and few pockets in northern areas of Turkey are less stable regions because of the low-correlated variance scores (below 10%). Furthermore, the impact of extreme phases of the ENSO (El Nino/La Nina) on droughts in four drought regions over Turkey is discussed.

Managing Municipal Water Supply and Use in Water-Starved Regions: Looking Ahead

In this editorial, the author shares 30 years of experience with water management in a semiarid region (specifically California). The focus of this writing is on municipal water supply; that is, water supplied by public water systems that support residential, commercial, industrial, and governmental users in populated areas. The editorial examines ways to improve the reliability of municipal water supply in water-scarce, fast-growing regions such as southern California. The challenges and the possibilities that arise concerning municipal water supply in southern California are not unique. They are similar in many parts of the world, whether it is northern China, the Middle East, or other drought-stricken regions. The author argues for unconventional approaches to help meet municipal water use in drought-vulnerable regions. A greater reliance on sustainable water sources, local in origin, is envisioned to diminish the dependence on imports and on the vagaries of the climate. Specifically, this editorial makes the case for reliance on “toilet-to-tap” sewage recycling and seawater desalination, both of which are herein shown to be unconventional sources of municipal water in California at this time. These two sources of water have excellent potential for stabilizing municipal water supply in drought-vulnerable regions.

Groundwater Constraints on Simulated Transpiration Variability over Southeastern Australian Forests

AbstractA land surface scheme with and without groundwater–vegetation interactions is used to explore the impact of rainfall variability on transpiration over drought-vulnerable regions of southeastern Australia. The authors demonstrate that if groundwater is included in the simulations, there is a low correlation between rainfall variability and the response of transpiration to this variability over forested regions. Groundwater reduces near-surface water variability, enabling forests to maintain transpiration through several years of low rainfall, in agreement with independent observations of vegetation greenness. If groundwater is not included, the transpiration variability matches the rainfall variability independent of land cover type. The authors’ results suggest that omitting groundwater in regions where groundwater sustains forests will 1) probably overestimate the likelihood of forest dieback during drought, 2) overestimate a positive feedback linked with declining transpiration and a drying boundary layer, and 3) underestimate the impact of land cover change due to inadequately simulating the different responses to drought for different land cover types.

Climate change impacts on spatial patterns in drought risk in the Willamette River Basin, Oregon, USA

Climate change is likely to lead more frequent droughts in the Pacific Northwest (PNW) of America. Rising air temperature will reduce winter snowfall and increase earlier snowmelt, subsequently reducing summer flows. Longer crop-growing season caused by higher temperatures will lead to increases in evapotranspiration and irrigation water demand, which could exacerbate drought damage. However, the impacts of climate change on drought risk will vary over space and time. Thus, spatially explicit drought assessment can help water resource managers and planners to better cope with risk. This study seeks to identify possible drought-vulnerable regions in the Willamette River Basin of the PNW. In order to estimate drought risk in a spatially explicit way, relative Standardized Precipitation Index (rSPI) and relative Standardized Runoff Index (rSRI) were employed. Statistically downscaled climate simulations forcing two greenhouse gas emission scenarios, A1B and B1, were used to investigate the possible changes in drought frequency with 3-, 6-, 12-, and 24-month time scales. The results of rSPI and rSRI showed an increase in the short-term frequency of drought due to decreases in summer precipitation and snowmelt. However, long-term drought showed no change or a slight decreasing pattern due to increases in winter precipitation and runoff. According to the local index of spatial autocorrelation analysis, the Willamette Valley region was more vulnerable (hot spot) to drought risk than the mountainous regions of the Western Cascades and the High Cascades (cold spot). Although the hydrology of the Western Cascades and the High Cascades will be affected by climate change, these regions will remain relatively water-rich. This suggests that improving the water transfer system could be a reasonable climate adaptation option. Additionally, these results showed that the spatial patterns of drought risk change were affected by drought indices, such that appropriate drought index selection will be important in future studies of climate impacts on spatial drought risk.

Identification of Agricultural Drought Vulnerable Areas of Tamil Nadu, India – Using GIS Based Multi Criteria Analysis

Though drought is normal part of the climate, vulnerability to drought depends on various climatic and physical factors. Information on the vulnerability to drought, helps in mitigation and drought proofing the region. This study aims at identifying the drought vulnerable regions of Tamil Nadu; India over agricultural area through Multi Criteria Analysis (MCA) under GIS environment. Major climatic, edaphic, biotic and social factors are considered. Each factor is classified into five classes and appropriate weights are assigned. The MCA under GIS environment was carried out and the results showed that the drought vulnerable region discerned by MCA mostly matched with the blocks identified by the Drought Prone Area Programme (DPAP) of Federal Government of India. Some blocks identified as drought vulnerable in this study and under DPAP had majority of area under forest. Some blocks of the state were found drought vulnerable in this study, which was not identified by DPAP.