Climatic factors affecting annual maize yields in the valley of Oaxaca, Mexico

Locally measured climatic variables, such as temperature and precipitation, clearly affect agriculture, particularly in semi‐arid regions. Some climate/agriculture applications, however, do better to focus on meso‐ and large‐scale atmospheric and oceanic circulatory influences on the location of interest. In the Valley of Oaxaca in the highlands of southern Mexico for example, rain‐fed maize yields are as sensitive to interannual variations in the Southern Oscillation Index (SOI) and a synoptic index of summer 850 hPa‐level temperatures in the Mexico–USA border region as they are to locally measured precipitation, a variable to which yields are also strongly related. From 1978 to 1990, August precipitation explains 62 per cent of the variation in yields on the area planted in rain‐fed maize in the Valley of Oaxaca, a region highly dependent on that crop. An index derived from 850 hPa‐level temperatures and the annual average value of the SOI are comparable, explaining 48 per cent and 68 per cent of maize‐yield variation respectively. This suggests that useful information for agricultural decision‐making in the Valley of Oaxaca can be obtained by monitoring ENSO and the development of large‐scale circulatory patterns. Unlike local observations, these larger scale phenomena may provide advance warning of precipitation conditions during the agricultural season upon which so many people's livelihoods in the region depend. © 1997 Royal Meteorological Society.