the management of supplementary irrigation for rainfed wheat during the drought periods using crop moisture index

abstract drought is one the most complicated and unknown natural disasters and rainfed agriculture is often the first sector to be affected by drought. in this research, we consider the drought monitoring from both meteorological and agricultural points of view. we have selected standardized precipitation index (spi) among the meteorological indices, with a one month time scale for the synoptic station of bojnurd. although there are few exceptions in during (1996-2005) in 1996, 1998, 1999, and 2000, in which the severely and extremely dry category have been matched to the growth season of the rainfed, the results of spi index from precipitation data of this station and the trend of drought variations from 1996 to 2005 show that in bojnord synoptic station, the meteorological drought has not happened in the growth season of the rainfed wheat (23 oct. to 17 june) or at least it has been near normal category. the periods from june 1998 to may 1999 and from june 2004 to june 2005 have been the driest and wettest periods, respectively. the meteorological indices such as spi, either are only the function of precipitation, or consider a long term time scale. in the first case they do not give a comprehensive analysis on the drought phenomena and cannot give be used for the monitoring of the crop moisture situation and in the later case, they are not applicable for short term time scales such as daily or weekly monitoring. therefore, to monitor the agricultural drought and influence the other factors such as the temperature along with precipitation, the crop moisture index (cmi) has been introduced for weekly monitoring. to achieve this goal, we have used the climatic data of bojnord synoptic station over ten years from 1996 to 2005. the results from cmi index show that in the last week of grain filling, around the last week of may, extremely drought (-2.7>cmi>-3) has happened. also, during the crop maturity, a exceptional drought has been monitored with cmi<-3. finally, we have given a schedule for supplementary irrigation of rainfed wheat in bojnord based on the critical periods of crop growth and according with drought monitoring. based on theory, is required to plan for 191 mm of supplementary irrigation around the grain filling.