Abstract. Accurate determination of past flooding characteristics is necessary to effectively predict the future flood disaster risk and dominant controls. However, understanding the effects of environmental forcing on past flooding frequency and magnitude is difficult owing to the deficiency of observations (data available for less than 10 % of the world's rivers) and extremely short measurement time series (<100 years). In this study, a numerical model, HYDROTREND, which generates synthetic time series of daily water discharge at a river outlet, was applied to the Yalu River to (1) reconstruct annual peak discharges over the past 1000 years and estimate flood annual exceedance probabilities and (2) identify and quantify the impacts of climate change and human activity (runoff yield induced by deforestation and dam retention) on the flooding frequency and magnitude. Climate data obtained from meteorological stations and ECHO-G climate model output, morphological characteristics (hypsometry, drainage area, river length, slope, and lapse rate), and hydrological properties (groundwater properties, canopy interception effects, cascade reservoir retention effect, and saturated hydraulic conductivity) form significant reliable model inputs. Monitored for decades, some proxies on ancient floods allow for accurate calibration and validation of numerical modeling. Simulations match well the present-day monitored data (1958–2012) and the
literature records of historical flood events (1000–1958). They indicate
that flood frequencies of the Yalu River increased during 1000–1940, followed by a decrease until the present day. Frequency trends were strongly
modulated by climate variability, particularly by the intensity and
frequency of rainfall events. The magnitudes of larger floods, events with a
return period of 50 to 100 years, increased by 19.1 % and 13.9 %,
respectively, due to climate variability over the last millennium.
Anthropogenic processes were found to either enhance or reduce flooding,
depending on the type of human activities. Deforestation increased the
magnitude of larger floods (100- and 50-year floods) by 19.2 %–20.3 %, but the construction of cascade reservoirs in 1940 significantly reduced their magnitude by 36.7 % to 41.7 %. We conclude that under intensified
climate change and human activities in the future, effective river
engineering should be considered, particularly for small- and medium-sized
mountainous river systems, which are at a higher risk of flood disasters
owing to their relatively poor hydrological regulation capacity.
Predicting the Future of Desertification in Tehran Province Affected by Climate Change and Human Activities
