Trend of water resource amount, drought frequency, and agricultural exposure to water stresses in the karst regions of South China

Frequent drought occurrences have adverse effects on the availability of water resources and have consequently caused growing risks of water-related stresses in the karst regions of South China. For better water management, we investigated the trend of water resources in the past five decades and analyzed the drought frequency distribution in these regions with the of regional water resource amount series. Moreover, we assessed the decadal variability in the agricultural exposure to water stresses in the karst regions of South China. Results indicated that water resources were had a lower amount in most provinces during 2000-2013. Compared with 1961-1999, 2000-2013 showed a decline of 1139.3 x 10(8) m(3) (8.51 %) in the average annual water resources. From the periodic pattern analysis, the periods 1987-1988 and 2009-2011 experienced a negative phase and the lowest amount of water resources in the cycle period of 20 years (dominant cycle period). The generated GEV distribution was a good fit to the probability distribution of extremely low water resource amount. Based on the analysis results, low water resource amount (lower than the value with a return period of 10 years) occurred 2.5 times on average in every province during 2000-2013. Moreover, the agricultural exposures to water stresses were investigated and found to exhibit different degrees of severity across regions and decades. The proportions of agriculture land areas exposed to water stresses in the 1960s, 1970s, 1980s, and 1990s are 39.31, 42.15, 41.28, and 45.78 %, respectively. In the 2000s, more and more agricultural lands (about 68.37 %) were exposed to water stresses, mainly in Yunnan, Guangzhou, Guangxi, and Sichuan. Particularly, large areas exhibited high agricultural exposures to water stresses in 2006 and 2009. The karst regions of south China are facing great challenges in managing water resources against droughts.