Drought is a complex natural hazard,and it is affected by many factors.Climate change brought about by global warming causes the intensification and increased frequency of drought,which triggers negative economic,social,and environmental impacts.Drought occurs frequently in China,resulting in considerable impacts and economic losses.The long-term ground-based observation data,meteorological drought indices and the non-parametric Mann-Kendall trend test were used to study the drought evolution in China during the period from 1961 to 2012.Drought monitoring worldwide has significantly progressed through various drought indices,such as the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI).The calculation of the SPI values is based on the statistical probability derived from precipitation data.The SPI can be flexibly designed to quantify the precipitation anomaly for a specific time period based on the long-term precipitation records for specific drought types.The SPEI is an improved drought index based on both precipitation and potential evapotranspiration (PET) data.SPEI considers the effect of reference evapotranspiration on drought severity,and retains the simplicity multi-scalar nature of the SPI which allows for the identification of different drought types.The multi-scale SPIs and SPEIs (e.g.,1,3,6,9,or 12 months) from all available weather stations were calculated using the long-term monthly precipitation and mean temperature data during the period from 1961 to 2012.The characteristics of drought including the frequency and its distribution as well as the proportion of area affected were analyzed based on these two meteorological drought indices.Results showed that SPI and SPEI with short timescales showed a high temporal frequency of dry and moist periods.The spatial patterns of drought severity change implicated by SPI and SPEI were basically alike,and these two indices could be used to characterize the regional drought conditions effectively.Additionally,the SPEI performed better in drought monitoring than the SPI,largely because the SPI values are based only on precipitation data,while the SPEI ones were based on both precipitation and temperature,and the very warm temperature during those decades may have an influence on the SPEI values.The SPEI values identified 17 drought events in both Guizhou and Ningxia during the period from 1961 to 2012,and the average durations of drought episodes in these two areas were 3 and 4.7 months respectively.The frequency distribution of drought showed that,compared with other time periods,drought occurred more frequently during the period of 2001-2010.The Mann-Kendall trend test was used to detect the trend of in situ reference data.A downward trend at high confidence levels was detected at 38 stations,and a nonsignificant downward trend of average precipitation was detected at most stations.The increase trend of mean temperature at high confidence levels and significant drying trend (in terms of the SPEIs) were detected at most of the stations in north China (Inner Mongolia,Hebei and Shanxi),northeast China (Liaoning,Jilin and Heilongjiang),northwest China (Shaanxi,Gansu,Ningxia,north Qinghai and southeast Xinjiang) and southwest China (southeast Sichuan,Yunnan,Chongqing and Guizhou).The drought area was in a significant enlargement trend in most of these zones.
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