The monthly，seasonal and annual average temperature series，precipitation in Yongchang during 1959－2009 was analyzed using linear and polynomial regression methods．The results show that the average temperature presented increasing trend，the abrupt change occurred in 1996 for temperature．The annual precipitation also showed increase trend since 1983，and during 1992－2009 annual precipitation was 20．6 mm more than climate average value，and abrupt change occurred in 1984 for precipitation．In the 1960s and the early of 1990s，it was relatively dry，the driest year in history occurred in this period，and during 1970－1978，1992－2009 it was relatively humid，the frost－free period prolonged since 1998，and it was gradually moving to the relatively warm and humid period．

regional heavy rain occurred in the middle of Hexi Corridor on August 18 2009 was analyzed from the synop tic situation,physical quantity fields, water vapor conditions and satellite image’s features. Results show that the development of 500 hPa blocking high from Balkhash Lake to Novosibirsk made the cold trough before the ridge strengthen and extend south, and it p rovided the cold air for this regional heavy rain. The western and northern extension of the subtrop ical high p rovided adequate water vapor for the rain. The convergence of the vortex at the level of 700 hP resulted in increase of upward airmovement, which p romoted convection unstable stratification emergence and development. The low and middle level instability energy triggered mesoscale convective activities in large -scale frontal rainfall cloud system , which was the main reason for this heavy rain event. The configuration of negative helicity at up level and positive helicity at low level has a good indication for forecasting heavy rainfall and rainfall area.

A local heavy rain occurred in the southernmountainous region of Yongchang County on July 14, 2006 was analyzed synthetically from several aspects of physical quantities, moisture condition, p recip itation intensity, satellite images and radar features. Results show that the wind shear convergence at the level of 500 hPa ismain factor resulting in thisweather event, and the wind vertical shear p rovides favorable conditions to ascent development of airflow; the convective cells caused by the external flow of vortex cloud system bring on this strong convective p recip itation. Meanwhile, we found that analysis on energy and Showalter index fields could be a good indication to strong convective weather forecast.

On June 27th，2005，the rocket rainfall enhancement operation was undertaken in Yongchang county of Gansu province，and the process was tracked and monitored by XDR digital weather radar. Through the analysis of synoptic background and radar echoes evolution before and after the rainfall enhancement operation，it was proved that under the favorable weather condition，after the rocket rainfall enhancement operation，the intensity of radar echo was increasing，the scope of radar echoes and the frequency of surface precipitation were enlarging，and the distribution of surface precipitation in 24 hours after the operation also confirmed the effect of this rocket artificial influence on rainfall.