Advances in separating effects of climate variability and human activity on stream discharge: An overview

Separating effects of climate change (ΔQc) and human activity (ΔQh) on stream discharge at the watershed scale is needed for developing adaptive measures to climate change. However, information is scarce in existing literature regarding whether such separating is feasible and whether reliable results can be produced. The objectives of this overview were to: (1) compare currently-used methods; (2) assess assumptions and issues of the methods; and (3) present a generic framework that overcomes possible issues. Based on the overview of fifteen recent representative studies, two methods can be used to estimate absolute magnitudes of ΔQc and ΔQh, while another method can be used to distinguish relative magnitudes of ΔQc versus ΔQh only. Because the methods' fundamental assumptions about baseline versus altered period, water storage change and deep groundwater loss, precipitation-runoff relationship, hysteresis influence of human activity, and record of time series can seldom be satisfied for many watersheds, it is more realistic and practical to distinguish relative effects than to estimate absolute magnitudes of ΔQc and ΔQh. Moreover, a generic framework was presented for gauged watersheds with negligible groundwater loss, aiming to avoid misuse of the methods in practice.