Scenario Analyses On Extreme Climate Events Over Ningxia

With global warming, more intense and longer droughts have been observed over larger areas since the 1970s, particularly in the tropics and subtropics. The frequencies of heavy rainfall events have increased over most of land areas. Widespread changes in extreme temperature have been observed over the last 50 years. Cold days, cold nights and frost have become less frequent, while warm days, warm nights and heat waves have become more frequent. It is of great significance to research the possible future changes in extreme climate events because the changes in frequency and intensity of extreme climate events will severely affect human and social activities to some extent.In this paper, the PRECIS, a regional climate model system developed at the UK Met Office Hadley Center for Climate Prediction and Research, is employed to address scenario projection for extreme climate events in Ningxia Provence. First of all, to validate PRECIS capacity to simulate spatial distribution and interannual variability of extreme climate events by comparing the extreme climate indices derived from simulation of PRECIS, which is driven by ECMWF 1979-1993 reanalysis data, with those from observed data. Secondly, to validate PRECIS's ability to simulate frequency of extreme climate events by comparing the Baseline (1961-1990) extreme climate indices derived from output of PRECIS with those from observed data. Thirdly, the correction methodology to simulated data of PRECIS is preliminarily discussed based on above validation, and is applied to scenario data. Finally, on the basis of correction to output of PRECIS, to analyse the changes of extreme climate events in the future (2071～2100) relative to Baseline under SRES A2 and B2 scenarios of IPCC.The main conclusion of this research can be summarized in the following items:(1) PRECIS has capability to simulate the characteristics of extreme indices of temperature and precipitation, but shows obvious overestimates in simulated temperature and precipitation comparing with observed data which cause the systematic bias between simulated extreme indices and observations. After correction to simulated data, the extreme temperature indices maintain their original fluctuation while the systematic bias has been reduced and the extreme precipitation indices are more consistent with observed data.(2) Relative to Baseline, in the last 30 years of 21st century, the annual extreme temperature would increase remarkably, and the increment under A2 scenario is larger than that under B2 scenario, and the increment in the northern region of Ningxia is larger than that in southern mountain area of Ningxia. Warm days and warm nights would increase notably and cold days and cold nights would decrease. The extreme temperature events under A2 scenario would change more severely than under B2 scenario. Warm days would increase remarkably and cold days would decrease in summer and autumn, while changes of warm days and cold days are not noticeable in spring. DTR would decrease, especially in winter and spring and in northern region. SU would increase remarkably, CFD would decrease remarkably, and GSL would extend. These three extreme temperature indices would change more acutely under A2 scenario than B2 scenario and would change more acutely in southern area of Ningxia than that in other areas. (3) Relative to Baseline, in the last 30 years of 21st century, the days of the extreme precipitation events would show a slender increasing trend as a whole, but annual changes are inconsistent and appear an interannual fluctuation. The extreme precipitation events would increase slightly in northern area of Ningxia, and would show fewer changes in southern area. The extreme precipitation events would increase a little in summer and autumn and change rarely in winter. Over Ningxia, R20mm, SDII and RX5day would increase a little, and the increment would be the largest in northern area. In addition, CDD would decrease, and decrease most in northern area.