Is April to July runoff really decreasing in the western United States

Several investigators have presented evidence that the ratio of April-July runoff to annual runoff has been decreasing in Western North America. The trend has been recognized both in rainfall-runoff and snowmelt-runoff streams. The decline in this ratio has been attributed to a change in the seasonal distribution of precipitation; there is concern that the changing ratio reflects a decrease in April-July runoff. Analysis of streamflow records for gaging stations that record natural flow confirms that the ratio has been declining at selected streamflow stations along the Pacific coast. The decline in the ratio, however, is by no means pervasive. Furthermore, tests for monotonic trend, while confirming a decline in the ratio, show no discernable trend in total April-July runoff, indicating that April-July runoff has not decreased. The trend in the ratio does appear to represent an increase in winter precipitation.