Abstract

The present research focuses on both past and future time scale in order to recognize the changes of effective precipitation trend in Ghazvin station. Therefore, in order to recognize the trend and behavior of past climate components, the components trend analysis have been done using Pierson and linear regression method. In order to study and analyze effective precipitation trend, the length of statistical data from 1959 to 2009 and data on climate temperature, precipitation, evapotranspiration, wind speed and radiation have been used. SCS method is used in calculating the effective precipitation. Also, the compound results of two models of CNRM-GISS-EH and CM3 have been used to evaluate the effect of regional climate change in the simulation of effective precipitation in 2050 and 2075 decades. The results of changes in effective precipitation trend for study period (1959 to 2009) indicates that the effective precipitation trend in spring is decreasing with the rate r=-0.10, however, the results in winter (r=0. 11), autumn (r=0. 24), and summer (r= 0. 16) indicates the increase of effective precipitation in recent decades. Also, it should be stated that the maximum increase of effective precipitation occurs in December with the rate 6 mm and the maximum decrease is in January with -1.91 in each decade. But, the average of the simulated results by the year 2075 indicates that the maximum decrease of effective precipitation is in July with 35.1% and the maximum increase will occur in August with 80.6%. Finally, however, the results indicate that the annual effective precipitation value in 2025 is increased with (1.7%) and in 2075 with (14.5%), but the great oscillation of these changes at summer, which is a dry period in Ghazvin, needs further management and planning for supplying the water requirement of different farming products, especially dry cultivation.

Key words: Climate change, carbon dioxide increase, dry farming, effective precipitation, SCS, Ghazvin.