Baoqing Zhang

A drought hazard assessment index based on the VIC–PDSI model and its application on the Loess Plateau, China

Drought is a complex natural hazard that is poorly understood and difficult to assess. This paper describes a VIC–PDSI model approach to understanding drought in which the Variable Infiltration Capacity (VIC) Model was combined with the Palmer Drought Severity Index (PDSI). Simulated results obtained using the VIC model were used to replace the output of the more conventional two-layer bucket-type model for hydrological accounting, and a two-class-based procedure for calibrating the characteristic climate coefficient (Kj) was introduced to allow for a more reliable computation of the PDSI. The VIC–PDSI model was used in conjunction with GIS technology to create a new drought assessment index (DAI) that provides a comprehensive overview of drought duration, intensity, frequency, and spatial extent. This new index was applied to drought hazard assessment across six subregions of the whole Loess Plateau. The results show that the DAI over the whole Loess Plateau ranged between 11 and 26 (the greater value of the DAI means the more severe of the drought hazard level). The drought hazards in the upper reaches of Yellow River were more severe than that in the middle reaches. The drought prone regions over the study area were mainly concentrated in Inner Mongolian small rivers, Zuli and Qingshui Rivers basin, while the drought hazards in the drainage area between Hekouzhen–Longmen and Weihe River basin were relatively mild during 1971–2010. The most serious drought vulnerabilities were associated with the area around Lanzhou, Zhongning, and Yinchuan, where the development of water-saving irrigation is the most direct and effective way to defend against and reduce losses from drought. For the relatively humid regions, it will be necessary to establish the rainwater harvesting systems, which could help to relieve the risk of water shortage and guarantee regional food security. Due to the DAI considers the multiple characteristic of drought duration, intensity, frequency, and spatial extent, and because it is based on the VIC–PDSI model and GIS technologies, the DAI could provide some new way on directly comparing the drought hazards over different regions during a long-term period. The result of this study may be useful to decision makers when formulating drought management policies to alleviate the risk of water shortages and guarantee regional food security.

Changes in key driving forces of soil erosion in the Middle Yellow River Basin: vegetation and climate

Severe soil erosion coupled with scarce water resources are two of the most important concerns related to the sustainable development in the Middle Yellow River Basin (Shi et al. 2012). Since the 1950 s, many soil and water conservation measures have been implemented in this region, including the construction of terraces, dams and reservoirs, and vegetation restoration (Ran et al. 2008). Notably, in 1999, a large-scale project (designated ‘‘Grain For Green’’) was initiated to control soil erosion and improve vegetation cover in this area by returning sloped farmland to forest or grassland (Zhang et al. 2013). As a result, several studies have reported that both sediment discharge and streamflow of the Yellow River Basin have been significantly reduced (Gao et al. 2012, 2013; Wang et al. 2007, 2010). Particularly in the past decades, the annual sediment load from the Yellow River delivered to the sea has sharply decreased from 16 9 10 to 1.5 9 10 t. Based on analysis of annual precipitation variation trends, Wang et al. (2007, 2010) reported that the decreases in precipitation were responsible for 30 % of the decreases in sediment load of the Yellow River Basin, while the remaining 70 % was ascribed to human activities, of which soil conservation practices (mainly included the construction of terraces, dams and reservoirs) since the late 1970 s contributed 40 % to the total decrease. With the effort of ‘‘Grain-for-Green’’ project since 1999, vegetation cover in the Yellow River Basin has exhibited overall increases (Zhang et al. 2013). Regions with sparse vegetation have declined sharply, mostly in the principal sediment source of the Yellow