Study on the Quantification of Drought in Freshwater Wetlands--A Case Study in Baiyangdian Wetland

Drought index is an important tool for monitoring and evaluation. A new drought index for freshwater wetlands is developed based on water balance, then used to evaluate drought in Baiyangdian Wetland (BW). Choosing the high resolution data--daily water stage (if not available, choose monthly data alternatively) as input data to compute the Wetland Drought Index (WDI). The results may be presented in monthly, seasonal or annual scale, such as Standard Precipitation Index (SPI). Daily data was used in calculating WDI during 1960 to 1986, and the results are revealed in monthly, seasonal and annual time scale to compare with SPI and China Z Index (CZI). The results of WDI are in accordance with the local record of wetland drought (Anxin county annals, 2000), while the other indices are not. Daily data produce the most precise dating of droughts, but these data were not available after 1986, therefore monthly data were used. For the period before 1986, comparisons using monthly data and daily data identify the same droughts, and show only minor differences in resolving drought onset and termination dates. During 1960 to 2008, the frequency of drought was increasing, mainly because of the low precipitation and controlling of reservoirs upstream. There are five mainly drought periods identified by WDI during this time: 1965 similar to 1967, 1972 similar to 1973, 1975 similar to 1976, 1980 similar to 1986 and 2000 similar to 2008, which are not identified by SPI and CZI.