Study On Spatial-Temporal Variations Of Precipitation Characteristics In Haikou City Under Changing Environment

Under the background of global climate warming and rapid urbanization, the spatial and temporal distribution characteristics of precipitation will be certainly affected in Haikou City which is an emerging capital city in recent 20 years. Based on the daily precipitation data collected from 8 precipitation stations in Haikou City during 1970 to 2012, the precipitation change features in the main urban area and the spatial- temporal variation characteristics of precipitation in the whole of Haikou City are analyzed using the methods of trend analysis, correlation analysis, Mann-Kendall mutation test, Morlet wavelets analysis and spatial interpolation method. Additionally, the influences of urbanization on precipitation are preliminarily studied in this paper. All above studies can provide information support for water resource planning, flood control and drainage and environment protection in Haikou City. The main results are as follows:(1) The annual rainfall has a trend to increase and the trend rate is 24.07mm/10 years in the main urban area of Haikou City in the recent 43 years. The annual precipitation fluctuates greatly and there are three periods which are 16 years, 8 years, 3 years and the 16 years is most obvious. The trend of precipitation in rainy season is similar to annual precipitation and the trend rate is 31.52 mm/10 years. Besides, the precipitation in rainy season also has three periods which are 17 years, 8 years and 3 years. In according with period analysis, it can be predicted that in the future there will be a state of more precipitation in the main area of Haikou City and more precipitation is expected to continue until around 2017.(2) In the main urban area the contribution rate of torrential rainfall to annual precipitation is 36%, more than other grade rainfall. The correlation coefficient is 0.501 between annual precipitation and moderate precipitation, 0.666 between annual precipitation and heavy precipitation, 0.869 between annual precipitation and torrential precipitation. They are significant at the 0.001 level, especially in torrential precipitation which has better indicative functions concerning the changes of annual total precipitation. It can be seen that the increasing annual rainfall is mainly induced by more torrential rain.(3) The annual distribution of precipitation is uneven and the majority of annual total precipitation and every grade precipitation occur in rainy season(May to October). In recent 43 years, light rainfall, heavy rainfall, torrential rainfall and annual total rainfall are all tending to focus on the rainy season and the tendency of torrential rainfall is particular obvious, which shows that an increasing number of strong rainfall events occur in rainy season in the main urban area and flood and waterlogging disaster is more likely to occur in this period.(4) The annual rainfall gradually decreases from southeast to northwest. Since 1970, the annual precipitation in southeast region presents an obvious trend of rising whose maximum rate is 8.5mm/year, while in central region there is an obvious downward trend which decreases 5.5mm every year at most. For most areas of the city, torrential rainfall has a trend to increase and precipitation for other grade tends to decrease. The uneven degree of precipitation mainly rise s in Haikou, and the tendency of annual precipitation concentrating in rainy season is more obvious in the main urban area and the southeast area. Moreover, extreme precipitation indices including maximum 1-day precipitation, maximum 3-day precipitation, maximum 5-day precipitation and maximum 7-day precipitation are mainly on the rise, and the rising tendency is also more obvious in the main urban area and the southeast area.(5) Urbanization does not make Haikou apparent “rain island effect”, but it exacerbates the uneven degree of precipitation distribution in a year. After 1990, the contribution of precipitation in rainy season to annual precipitation increases by 5.6% in the main urban area and the proportion of torrential rain increases more significantly. So the probability of occurrence of extreme precipitation events increases in the main urban area. Besides, the variation coefficient of maximum 1-day precipitation increases by 0.14 in the main urban area, which will affect the standard of existing and planned urban drainage engineering and the flood drainage design.