A Hydrometeorological Perspective on the Karakoram Anomaly Using Unique Valley-Based Synoptic Weather Observations

Abstract

Glaciers in the eastern Hindukush, western Karakoram, and northwestern Himalayan mountain ranges of Northern Pakistan are not responding to global warming in the same manner as their counterparts elsewhere. Their retreat rates are less than the global average, and some are either stable or growing. Various investigations have questioned the role of climatic factors in regard to this anomalous behavior, widely referred to as "The Karakoram Anomaly." Here, for the first time, we present a hydrometeorological perspective based on five decades of synoptic weather observations collected by the meteorological network of Pakistan. Analysis of this unique data set indicates that increased regional scale humidity, cloud cover, and precipitation, along with decreased net radiation, near-surface wind speed, potential evapotranspiration, and river flow, especially during the summer season, represent a substantial change in the energy, mass, and momentum fluxes that are facilitating the establishment of the Karakoram anomaly. Plain Language Summary The "Karakoram Anomaly" is a term that is used to describe the fact that glaciers in the eastern Hindukush, western Karakoram, and northwestern Himalayan mountain ranges of Northern Pakistan are not responding to global warming in the same manner as their counterparts elsewhere. Specifically, their rates of retreat are less than the global average, and some of the glaciers are either stable or even growing. This remarkable phenomenon has therefore become a popular news topic, and even an excuse for some people to question whether global warming is actually occurring. Our analysis of in situ hydroclimatic variables and river inflows indicates that there is a clear scientific explanation for this localized phenomenon. It is true that glacier melt contributions to river flows during the summer season are decreasing, in spite of the fact that the precipitation has been increasing. But the reason that the glaciers in this region are not melting at increased rates is that summer season cloudiness has increased, which blocks the incoming solar radiation and thereby lowers the amount of heat energy available for the melting process. Combined with the facts that humidity has increased and near-surface wind speeds have decreased, this has also resulted in reduced moisture loss through evapotranspiration. Together, these conditions have resulted in reduced rates of glacier melting in this region. These findings explain and support the fact that "Karakoram Anomaly" is a real, albeit localized, phenomenon.