Abstract
Drought is a complex phenomenon caused by lack of precipitation that affects water resources and human society. Groundwater drought is difficult to assess due to its complexity and the lack of spatio-temporal groundwater observations. In this study, we present an approach to evaluate groundwater drought based on relatively high spatial resolution groundwater storage change data. We developed an artificial neural network (ANN) that employed satellite data (Gravity Recovery and Climate Experiment (GRACE) and Tropical Rainfall Measuring Mission (TRMM)) as well as Global Land Data Assimilation System (GLDAS) models. The Standardized Groundwater Level Index (SGI) was calculated by normalizing ANN-predicted groundwater storage changes from 2003 to 2015 across South Korea. The ANN-predicted 25 km groundwater storage changes correlated well with both the in situ and the water balance equation (WBE)-estimated groundwater storage changes, with mean correlation coefficients of 0.87 and 0.64, respectively. The Standardized Precipitation–Evapotranspiration Index (SPEI), having an accumulation time of 1–6 months, and the Palmer Drought Severity Index (PDSI) were used to validate the SGI. The results showed that the SGI had a pattern similar to that of SPEI-1 and SPEI-2 (1- and 2-month accumulation periods, respectively), and PDSI. However, the SGI performance fluctuated slightly due to its relatively short study period (13 years) as compared to SPEI and PDSI (more than 30 years). The SGI, which was developed using a new approach in this study, captured the characteristics of groundwater drought, thus presenting a framework for the assessment of these characteristics.
Highlights
Accelerated global warming, resulting in drought and floods, has significant impacts on the hydrological environment on a global scale
We suggested the criteria for the Standardized Groundwater Level Index (SGI) using percentile of groundwater storage changes, such that SGI ≤ −1.5 corresponded to exceptional drought, −1.5 < SGI ≤ −1.2 was denoted as extreme drought, −1.2 < SGI ≤ −0.9 corresponded to severe drought, −0.9 < SGI ≤ −0.6 was moderate drought, −0.6 < SGI ≤ −0.3 was seen as abnormally dry conditions, and SGI > −0.3 as corresponded to normal/no drought
Groundwater storage changes with changing precipitation are generally low in the dry season and high in the wet season
Summary
Accelerated global warming, resulting in drought and floods, has significant impacts on the hydrological environment on a global scale. The Korean Peninsula has recently experienced an increase in annual precipitation; the number of days of precipitation has decreased, and there has been a serious local drought phenomenon. Droughts continue to occur and have caused environmental and socio-economic losses. In recent years (2014–2015), the Central and Kangwon. Provinces have suffered severe droughts that have affected surface water (e.g., reservoirs, lakes), and groundwater. The groundwater level in Jeju Island was found to be much lower than normal due to drought during these years. Damage caused due to groundwater drought is not restricted to domestic water, and includes agriculture and industry. Research related to the understanding and prediction of groundwater drought is increasingly important
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