The spatial and temporal distribution of point precipitation quantiles representing abnormal moisture conditions over the Colorado River Basin (CRB) is analyzed by means of the Standardized Precipitation Index (SPI), calculated in annual and seasonal aggregations. From a cell-by-cell analysis, the area covered by abnormally wet and dry conditions during the last century shows an inverse relationship with their frequency of occurrence, with frequent events (occurring 80% of the time) in which abnormal conditions cover less than 10% of the basin and infrequent events (occurring 5% of the time) in which abnormal conditions cover around 50% of the basin. During El Ni�o years, both extremely wet and dry conditions are likely to occur, while [...]
