Spatial and temporal trend continuity analysis of the correlation between yield and rain and drought

Managing the impacts of rain and drought on agriculture depends on the degree of accurate monitoring of these effects. For accurate monitoring, this study investigated the impacts of rain and drought (using the reconnaissance drought index (RDI)) on agriculture during different moving periods (MPs) using various time scales (seasonal and annual). This investigation was done by estimating correlation coefficients (CC) between winter wheat yield and rain value (CCYR) and between yield and RDI index (CCYRDI), trend analysis of these CCs, and estimating correlation coefficients between the time series of the temporal trend of yield (TCY) and rain (TCR) and RDI (TCRDI). The results of considering CCYR indicated similar changes for Winter and Annual time scales and opposed changes for Autumn and Winter and for Spring and Winter. The results of considering CCYRDI indicated similar changes for Winter, Spring, and Annual time scales and opposed changes for Autumn. As the moving period increases from 10 to 20 years, the similarities increased and oppositeness decreased. The results of CCYR and CCYRDI trend analysis showed the reduction in these coefficients that generally indicate the reduction of effective rain for crop production and increase in drought during recent MPs.The results of estimating correlation coefficients between TCY and TCR indicate the importance of spring rainfall in the north and winter rainfall in the south of the study area. The results of estimating correlation coefficients between TCY and TCRDI indicated that the highest values of correlation coefficients, were obtained in the spring season.