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New paper! We tried to better understand why some glaciers in Asia are growing by combining different models and datasets. With @philipkraai, @pleunbonekamp, Obbe Tuinenburg, @immerzeel ( @UU_PhysGeog @UUGeo @UUCopernicus) https://tc.copernicus.org/articles/14/3215/2020/ 1/15
Short answer: irrigation seems important, but also the Caspian Sea and the relatively low temperature sensitivities of the glaciers seem to play an important role in making these glaciers grow. 2/15
Growing glaciers are rare, considering global warming. but they exist in a region in Asia, a phenomenon often called the ‘Karakoram anomaly”. Why are glaciers are growing in some places, but not in others? We first looked at how the weather has changed in the last decades. 3/15
When we started, the spatial resolution of available data on past weather weren’t great for High Mountain Asia, so we used the WRF regional climate model. We also included irrigation, which we previously found to be potentially important for mountains https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076158 4/15
Our model output shows a warming trend in the melt season for most glaciers, but some glaciers have an increase in snowfall. 5/15
We tried to see what this does to the glaciers by feeding our climate model output into a glacier mass balance model. The pattern of glacier mass balances in High Mountain Asia from the model matches the observed one pretty well, with growing glaciers in the right places. 6/15
In our model, it’s the increase in snowfall that causes the glaciers to grow, not a decrease in temperature, but the growing glaciers do seem less affected by rising temperatures. So we asked: what causes that increase in snowfall there and a decrease close by? 7/15
We used a moisture tracking model to see where the moisture associated with the snowfall first entered the atmosphere to see where there was an increase of moisture supply. 8/15
We found that the irrigation areas near the mountains are an important source of increasing moisture. Another source is the Caspian Sea, but that also increases snowfall in regions where glaciers are shrinking and total snowfall is decreasing. 9/15
So, we still think increases in irrigation from agriculture is an important contributor to the growing glaciers in High Mountain Asia. 10/15
Models like ours are always imperfect. In the future, it would be good to improve the irrigation modelling, and model specific regions at very high spatial resolution. 11/15
Importantly, we need more and better measurements in the region of growing glaciers. Almost no data exists there, which makes our knowledge of the region, and model studies such as ours, quite uncertain. 12/15
Such model uncertainty is inevitable with a lack of data, but it has caused us great trouble publishing this paper, even though we think the model is reasonable (in the end it's all forced with reanalysis data, which includes many observations) and adds new insights. 13/15
We added multiple comparisons with different datasets that cover regions close by. Everything indicates that our model does a reasonable job in representing the weather in the region. Would be great if others also do similar modelling with irrigation included, though! 14/15
So, hopefully our work also inspires some future work from other groups to better understand the growing glaciers of Asia. For many more details and arguments, please check out the paper! 15/15