Rainfall Fluctuation for Exploring Desertification and Climate Change: New Aridity Classification

The research community in Jordan is basically relying on universal defined aridity classifications, which do not consider the local conditions of Jordan and climate change effects on Jordan. The present study aims at producing a customized aridity classification that better fits the conditions of Jordan. Monthly rainfall data for the period between 1961-2012, for 22 weather stations covering the whole country, were obtained from Jordanian Meteorological Department (JMD). A ten-year moving average was calculated and used for conducting a historical trend analysis and generating aridity spatial maps. Monthly, annual, and ten years moving average aridity trends were tested using Tukey test, Mann-Kendall rank, and a simple linear regression. According to the historical trend analysis, rainfall across the country is significantly ( 0.0001) spatially and temporally distributed, where 90% of the country falls within arid to semi-arid classes. Climate change impacts in Jordan resulted in a shorter rainy season with lower amounts of precipitation and the number of rainfall events. The overall annual rainfall tended to decrease significantly (P 0.05) by time with an average reduction rate of 1.1 mm per year. Although the overall trend for most of the rainfall stations was decreasing, individual annual rainfalls analysis indicated the possibilities of extreme events to occur at some locations. The overall trend showed that more frequent drought seasons are expected. According to the new generated aridity classification maps, the country is suffering from a severe shifting to lower rainfall means. The southern and the northern-eastern parts shifted from strongly arid (100-150 mm) into hyper arid class ( 100). Moreover, west-middle part also shifted to moderately arid class (150 – 200 mm). On the other hand, the most obvious shift occurred at the semiarid classes especially the slightly and moderately subclasses. Currently, the wettest two classes (sub-humid and slightly semi-arid) are not present in the map and shifting towards a strongly semi-arid class.