[1] Frequent measurements of stream chemistry during snowmelt and summer storms were used in three watersheds that differ in permafrost coverage (high, 53%; medium, 18%; and low, 4%) to determine the role of water flow paths on the fluxes of carbon, nitrogen, and major solutes from Alaskan catchments. Permafrost was important in the seasonal pattern of stream chemistry as there was a distinct shift in chemistry and flow from winter through snowmelt and into summer in the permafrost-dominated catchment. Furthermore, the active layer above the permafrost was important for the late summer release of NO 3 À and DOC, suggesting a deeper active layer may increase N and C loss in permafrost-dominated areas. Overall, permafrost constrained water flow to the active layer, resulting in higher DOC but lower dissolved mineral fluxes (Ca 2+ Mg 2+ K + Na + ) in the high-permafrost watershed than in the watersheds with less permafrost coverage. However, the decline in dissolved mineral fluxes was not linearly related to permafrost coverage across watersheds. The flux of weathering ions may also be explained by total water runoff, since the medium-permafrost watershed, which had the greatest runoff on an areal basis, yielded the greatest loss of all major elements (Ca

Southwest Western Australia (SWWA) has experienced a 15–20% reduction in rainfall since the 1970s with severe reductions in inflows to Perth drinking water reservoirs. To quantify rainfall and runoff patterns, we used trend and change point analyses for a 50 year record (1950–2008) and in the last two decades (1989–2008). From 1950–2008, trend tests showed significant declines in annual rainfall and runoff with corresponding change points for both rainfall and flow in the late 1960s or mid‐1970s. In the more recent record (1989–2008), runoff declined in the majority of catchments, but rainfall did not show a significant downward trend. Rather, streamflow decline was observed as a step change in response to the occurrence of below‐average rainfall years. A shift from perennial to ephemeral streams and a decline in the runoff coefficient (runoff/rainfall) in the last decade suggests a new hydrologic regime has developed with important implications for future surface water supply.

In this study we examine the hydrological processes that underpin non‐stationarity in hydrological prediction. This is achieved by analysis of linkages between rainfall, groundwater storage, and runoff in Southwest Western Australia (SWWA), a region experiencing stream flow decline since the mid‐1970s. We find a close connection between rainfall and changes in catchment groundwater storage, with increases in storage in years with annual rainfall above a threshold (1050–1400 mm), and declines during low rainfall years. Where groundwater is in contact with the stream bed, runoff, as a proportion of rainfall, is highly correlated with groundwater storage. Recent drought years have reduced groundwater storage and runoff ratio. In the absence of replenishing wetter years, lower runoff ratios are subsequently maintained. Runoff from a given depth of annual rainfall is now far lower than that produced 15 years ago. In this way groundwater storage acts as the catchment's “memory”. This study highlights the importance of catchment groundwater storage that may be used to improve runoff prediction in a drying climate.

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