2.2.3. Observed Data

The climate station network in the UIB has historically been comprised of only a few low-altitude, valley-based stations. Although the number of in situ observational points has increased since the mid-nineties, with the installations of a few higher altitude automatic weather stations, the coverage is still very thin, and the data is often not very representative, especially for different elevation zones. Similarly, while most of the weather stations have become operational after the mid-nineties, long-term data is a rare commodity and is only available at limited locations.

Similarly, owing to the complex orography of the UIB region and to the co-action of different hydro-climatic regimes, neither the sparse observed station data or the gridded data products based on them, nor the sensor-based climatic datasets fully represent the precipitation regime of the region [6, 16,27,28]. Several studies have pointed out that precipitation and other climatic variables in the HKH region exhibit large changes over short distances and considerable vertical gradients [11,29–34].

In the absence of long-term climate data with acceptable representation of the UIB climate, most climate-change studies have relied on either the very thin climatic observation network records or the gridded datasets based on them. In all these cases, either the data have acceptable quality, but shorter duration, or they have huge biases, especially, in the case of precipitation in regions with higher altitudes. These biases are further amplified when this data is used as a reference for bias correction or downscaling of climate projections, making the results questionable.

In the current study, therefore, a new long-term climate dataset was prepared (Figure 2). The work related to this new long-term gridded data product [7] is not included in this paper, but we utilized this new dataset instead of the readily available global or regional gridded historical climate datasets, for bias correction, downscaling and assessment of the reliability of climate models for the simulation of the past climate in the region.

These gridded precipitation and temperature data are derived, based on all the available in situ observations available in the UIB, through reconstruction for the periods before the mid-nineties, interpolation and correction for the orography and elevation-induced effects guided by available data for runoff, actual evapotranspiration and glacier mass-balance [7].
