The Modification And Application Of Palmer Drought Severity Index In Huaihe Area Basin

Palmer Drought Severity Index (PDSI) based on water balance principle is meaningful in physics.So PDSI could not only indicate the drought severity degree, but also when the drought would occurre. But the modification should be done because of the spatial discontinuities.The results of comparing the drought condition in Huaihe River Basin and the USA Southeas t region, as well as several modified Palmer index results show that the drought/wet conditions in different areas would affect the condition later differently. And based on the conventional surface observations daily temperature, wind, sunlight hours and other information from36stations there, a modification of PDSI with appropriate adjustment of the influence of early period drought/wet condition is carried out to indicate the drought/wet more accurately. A few of discussions about the distribution characteristics of the annual or seasonal precipitation and temperature in Huaihe River Basin was carried out with the Mann-Kendall mutation testing, moving t test, Morlet wavelet analysis and so on.Using NCEP/NEAR monthly wind and geopotential height field, the analysis of circulation anomaly in flood and drought years in the Huaihe River Basin caused by South Asia high were investigated,and the results show that:(1) Because of the sensitivity of an area to precipitation changed when it was in different drought/wet grade, appropriate adjustment of the influence of pre-period in the calculation of PDSI, the results reflect the drought or flood more accurately.(2) The area index based on Palmer Drought Severity Index distributions showed that in the recent50years, the area index based on Palmer Drought Severity Index distributions showed that the climate condition trends for winter, spring, summer, autumn were more wetter-drier-wetter-drier in the whole of Huaihe River basin. And this coincided with the increasing (decreasing) frequency and intensity in precipitation in summer (spring and autumn). There was a good coincidence between the drying trend in spring and the spring event happened earlier properly in the IPCC report in2007. The evaporation increased because of the tempreture rising, or the indirect effects of temperature rising may promote drought condition in spring.(3) It would be different that different index reflecting thedroughts/flood condition due to the Index mechanism in the same area. With the consideration of both the current rainfall anomalies and pre-period moisture conditions, PDSI showed well response to the cumulative effect of drought/flood.The precipitation variability would influence the response to climate condition with different index.(4)There were obvious drought periods in summer while the drought situation was different in Huaihe River Basin. The rainfall and rainstorm in summer fluctuated slightly, and peak drought was obvious in1966-1978.Otherwise,the rainfall and rainstorm in summer fluctuated greatly, and arid distribution by PDSI index was relatively smooth in1992-1999.The temperature dropped down sustaintly in1966-1978, and a warming period in1992-1999. It could be inferred that the temperature increasing was likely to promote the extreme precipitation, therefore, temperature change would not only impact on the drought through evaporation directly, but also on extreme precipitation indirectly.(5) Analysis of the circulation and water transportation abnormally were carried out based on monthly NCEP winds field, geopotential height field and specific humidity field. The east Asia influenced by the South Asia High especially through the area at110°E-140°,35°N-50°N. There was good coincidence between the South Asia high anomaly at100hPa and the drought/wet condition in Huaihe River Basin, and a good sigh for subtropical high anomaly. And the South Asia high may reflect the circulation above Huaihe River though the troposphere and stratosphere interactions. The South Asia high anomaly happened mainly in the early summer, and the subtropical high anomaly in the later summer, and it showed well that the South Asia high may be a good sigh for the climate anomaly.