A Study On Relationship Between Precipitation-Concentration Degree And Drought/Flood In Ningxia

The south part of Guyuan in Ningxia is belong to semi-humid temperate zone, the region from the north part of Guyuan to Yanchi and Tongxin is belong to concentric area in temperate semi-arid, Yellow River irrigated area is belong to the temperate zone. Drought is the most important climate characteristics of Ningxia, and is the biggest weather disasters for economic development and people’s life. But in the context of90%years are drought in Ningxia, is still frequent storms and floods. Therefore, accurate prediction of droughts and floods around the trend of Ningxia, a reasonable arrangement for industrial and agricultural production, while avoiding disadvantages, revitalizing the local economy, has an extremely important role.Precipitation-Concentration Degree(PCD) and Precipitation-Concentration Period(PCP) can well characterization of the degree of Precipitation aggregation and Precipitation accumulation, and play an important role in the research of the trend of droughts and floods. Based on the data of pentad precipitation from the main stations in Ningxia from1961to2010in this paper, calculate the PCD, PCP and Z index in the year,spring, summer and fall, and study the characteristics of temporal and spatial distributions of PCD, PCP and the degree of flood and drought used the methods of trend analysis, correlation analysis, composite analysis, M-K(or Lepage) test and Mexico-hat wavelet. By using the NCEP/NCAR monthly mean reanalysis data from1961to2010, the characteristic impact of Arctic Oscillation and South China sea monsoon against PCD and degree of flood and drought is discussed. The study in this paper is expected to reveal the law of the changes on precipitation, provide the basis for the Ningxia drought and flood forecasting.(1)The space distribution features of precipitation-concentration period (PCP) and precipitation-concentration degree (PCD) are obvious in Ningxia. And concentration degree of a year, spring, summer, autumn and its standard deviation are decreasing from the north to the south, the same as concentration period standard deviation. The possibility of extreme precipitation appears and temporal variability of heavy rainfall are larger in north. From1961to2010,a year, summer PCD and PCP are slow down, spring PCP is no obvious increase and PCD are rising, autumn has no obvious change trend. Nearly10years, a year, spring, summer and autumn PCD increased obviously, a year, spring and summer PCP delayed. (2) The drought grade of spring, summer, autumn and a year in Ningxia has been being increased for50years. And the precipitation-concentration degree (PCD) of spring, autumn and a year has great effect on drought.The higher the PCD is, the less the probability of flood is and the less the PCD is, the higher the probability of drought is. But the PCD in spring has little effect on drought. However, that the first soaking rain of spring comes sooner or later affects the drought in spring a lot, and the earlier the first soaking rain appears, the more rain there is. On the other side, the later the first soaking rain appears, the less rain and higher drought degree there is in spring.(3)The date of the first soaking rainfall delays from south to north in spring and has no obvious variation trend for50years. There has been a comparatively late stage since2000. When the soaking rainfall early, Ningxia is in the place that positive and negative departure converges on500hPa height fields, so cold air can continue to enter in. Meanwhile, plenty of water vapor can be brought from bay of Bengal. When the soaking rainfall later, controlled by northwest cold air before ridge from the lake Baikal with small water, Ningxia has no obvious precipitation.(4) The impact of Arctic Oscillation in high latitudes and South China sea monsoon in low latitudes against Ningxia Precipitation-concentration is distinguished. Annual precipitation around Ningxia is concentrated in the years that Arctic Oscillation is weakness or South China sea monsoon onset earlier, and flood is more likely. The location of the subtropical high from July to August has a distinguished impact on the flood and drought in Ningxia. The subtropical high is southern of its mean position, and vice versa.(5) Meanwhile the sea level pressure is low in the west and high in the east, and850hPa Western Pacific Subtropical High in the east side of Northwest China is controlled by southeast airflow on autumn flood period, and drought period on the contrary situation.