ABSTRACT. The tropical glaciers of the Cordillera Blanca, Peru, are rapidly retreating, resulting in complex impacts on the hydrology of the upper Río Santa watershed. The effect of this retreat on water resources is evaluated by analyzing historical and recent time series of daily discharge at nine measurement points. Using the Mann-Kendall nonparametric statistical test, the significance of trends in three hydrograph parameters was studied. Results are interpreted using synthetic time series generated from a hydrologic model that calculates hydrographs based on glacier retreat sequences. The results suggest that seven of the nine study watersheds have probably crossed a critical transition point, and now exhibit decreasing dry-season discharge. Our results suggest also that once the glaciers completely melt, annual discharge will be lower than present by 2-30% depending on the watershed. The retreat influence on discharge will be more pronounced during the dry season than at other periods of the year. At La Balsa, which measures discharge from the upper Río Santa, the glacier retreat could lead to a decrease in dry-season average discharge of 30%.

The response of a fractured bedrock aquifer in a temperate region (Gulf Islands, British Columbia) to heavy rainfall events is characterized. Of the 14 provincial observation wells with hourly groundwater level data, wells with shallow water levels showed pronounced responses to heavy rain events, a lag less than 12 hours, and a strong correlation to all rain events. Rises in groundwater level at Well 125 appear to be better related to all rain events than exclusively heavy rain during summer, and decrease as the rainfall intensity increases. Thermal infrared images and δ 18 O and δ 2 H composition for precipitation and seepage indicate an increase in seepage in the late fall and winter.Solution of the Green-Ampt equation for rainfall events of varying magnitude suggest that an increase in winter rainfall intensity leads to more surface ponding and overland flow. The projected occurrence of more heavy rain events in the future may result in lower net recharge.