Study On The Application Of The Drought Indicators Over The Arid Areas In Northern China

Drought is one of the main climate disasters in northern China. Drought prediction, monitoring is a challenging task. In this paper, taking Wuhai in central and western Inner Mongolia as the represented weather station, we analyze the climate characteristics of the drought in north arid areas in China is analyzed by three drought indicators, such as precipitation anomaly percentage index, Z index and M index, using precipitation, temperature and evaporation data at Wuhai weather station from 1961 to 2006. The results are as follows:(i) There are different levels of drought occurred in each year at Wuhai of the arid area northern China, particularly in spring, severe drought phenomenon almost occurred and drought process is more complex.(ii) For the typical arid region with less precipitation north, and the uneven distribution of rainfall time, the results of the three drought indexes are quite different by being compared with the actual situation. Overall, three indicators are more light than the actual situation, showing more predictions of non-drought years and seasons. On the year and season scale, for severe drought, Z index and M index obviously give lower level, and M index is particularly prominent. For the discrimination of drought and non-drought, the precipitation anomaly percentage index shows better consistency with M index, but Z index shows big difference. On the month scale, the three indicators show big difference on the discrimination of the wetter month and drier month. Overall, on the discrimination of the wetter month, the precipitation anomaly percentage index shows better consistency with Z index, and on the discrimination of the drier month, the precipitation anomaly percentage index shows better consistency with M index. For the discrimination of the severe drought, the results of the precipitation anomaly percentage index show consistent better with the facts ,and the results of Z index and M index give lower level, especially M index.(iii) In the arid regions of northern China, three drought indexes have higher dependent on time scales in drought levels classification. Comparatively, Z index and M index have less dependence on the time scale. Due to the distribution of rainfall time is uneven and precipitation variability is larger, therefore, for Z index, on the discrimination of drought, the longer time scale, the better the effect of discrimination; The shorter time scale, the worse the effect. Therefore, in arid areas of north China, the drought discriminant by the Z index on monthly scale does not occur, and the difference among the actual situation will be arises over the omission of the phenomenon, showing the instability of calculation. Therefore, Z index is not suitable for drought analysis for the arid regions of northern China. For the discrimination of a drought and a non-drought year, M index shows better consistency with the precipitation anomaly percentage index. But, for the discrimination of severe drought on annual, season and month scales, M index give lower level and is particularly prominent in the less rainfall season and the month with the discriminant results without severe drought having to do with the actual situation. On the analysis of the drought on month scale, the drought classes by M index are not good, sometime high and sometime low. representation stability is not available, Therefore, M index is not suitable for drought analysis for the arid regions of northern China.(iv) Comparatively, because it has simple calculation and is easily into the day-to-day operational forecasting, the precipitation anomaly percentage index is suitable for drought analysis for the arid regions of northern China. With precipitation anomaly percentage applied in Wuhai drought prediction, the drought classes show lower than the actual situation. Therefore, the drought class standards have been adjusted on different time scales according to the actual drought of Wuhai areas. Based on revised drought class standards, the drought situation in Wuhai was analyzed. Results show that at Wuhai areas, drought occurred in eight years every decade, and one of the droughts is very severe drought. Seasonal drought occur once every two years; the frequency of very severe and severe droughts in spring abode in the first quarter, and the percentage of the two droughts is about 50%.In the droughts of March to October, the frequency of severe drought from March to May abode in the first, and the percentage of the two droughts is over 50%; There are no severe droughts in July and September, because July, August and September are the wettest months, the percentage of severe and severe droughts is from 9% to 11 %, which is the least in a year. The results above are better consistent with the actual situation.