Can long-term landscape change predict the impact of extreme events? A test from the flashfloods of the upper Indus Valley, Ladakh, 6th August 2010.

Communities based in mountainous regions of the world are always susceptible to debris flows, mudflows and landslides. Such events are commonly triggered by intense rainfall as has been the case for this summer's Indian monsoons which has caused huge surges of mud and debris down the valleys of the usually arid landscapes that border Tibet. In the town of Leh in the Ladakh region of NW India, more than half of their annual rainfall fell in one hour on the 6th August, and the mud and debris killed 185 people and left 500 missing. Climate model predictions suggest that these types of events in this region are likely to double over the next 60 years. Therefore, it is vital that we consider ways to mitigate and adapt for future scenarios, and that this must involve improved understanding of the processes, and the likelihood of a similar event happening in the near future. Fortunately, researchers at the University of Edinburgh have been surveying the exact river catchments that have been responsible for this summer's devastation. Based on these surveys, they have built sophisticated models of the evolution of the landscape over the last 100,000 years. Using these models they can predict the long-term distribution of river downcutting and the accumulation of mud and rock; the question is 'can models that are based on the time-averaged trajectory of landscape change be used to predict the impact of extreme events?' This question can be answered by re-surveying the exact sections of the river valley that had been measured three years ago, and recording where rivers have downcut, where hillslopes have collapsed and where mud and rocky debris have accumulated. If the landscape change following this summer's events is similar to the pattern of long-term change, then the impact of this event is predictable from the current models, and further analyses will be able to estimate the likelihood of a similar event happening again. If the re-surveys show that the signal of landscape change is different to the long-term pattern, then it will highlight the dangers of follow-on events linked to the reorganisation of the landscape back to its more stable form. For example, if the rivers have incised deeply, forming steep gorges, then the probability of collapse of the gorge walls will be increased. In contrast, if the river channels have accumulated lots of sediment, then the likelihood of flooding is increased as water is displaced onto the floodplains. This post-event legacy of landscape change is vital for the communities dependent on the rivers for their drinking water and irrigation in this arid environment. Clearly, if the rates of long-term landscape change are known, then the significance of this summer's event can be assessed. Once again, the researchers at Edinburgh have been fortunate in that the age of many of the geomorphological landforms such as moraines has been dated at around 100,000 years ago. For this project, the team intend to improve the measurement of this age in order to get better resolution on the time averaged rates of landscape change in the region. Having done this, the relative significance of this event can be assessed. Having better understood the redistribution of sediment and rock generated by this event, and the likelihood of it being repeated in the near future, the Edinburgh team aim to hold local workshops in the town of Leh with help from their colleague Dr Shakil Romshoo at the University of Jammu and kashmir. Their hopes are that by discussing their findings with government and non-government bodies, they will help local communities develop policies for mitigation and adaptation against future events.