Total Basin Run Off (ESA POLAR+ 4D Greenland Experimental Dataset)

The total monthly runoff (2014-2021), both surface and basal, of five drainage basins in Greenland; NEGIS, Northern Lakes, Southern Lakes, Store, and Watson. The run off is estimated by summing the Surface Melt, Firn Retention, Supraglacial Change and Subglacial Runoff into monthly basin scale estimates.
1. Surface water was computed from the chosen RCM on a monthly basis by summing the surface melt and the liquid precipitation (rain fall).
2. Firn Retention is computed by subtracting the RCM runoff from the RCM surface melt in the snow/firn-covered part of the drainage basins
3. Supraglacial change volume estimates were determined via the following methodology by Lancaster University.
Supraglacial lake extent were delineated using RT algorithm to classify water within S2 images. Lake depths were calculated using a radiative transfer model (section 2.2.6.1 ATBD). Lake depth was determined using Sentinel 2 red band imagery (Band 4). Total lake volume was calculated by multiplying lake depths by lake area for each individual lake polygon and summing over the basin area.
Volume uncertainty was determined via comparison with ICESat-2 transects. The uncertainty is represented by the maximum percentage difference between lake depths integrated over ICESat-2 transects and the corresponding S2 derived lake depth transect. For the red band, it was found that lake volumes were being underestimated by up to 33.5%.
Some of the meltwater in the supraglacial lakes will not leave the ice sheet at the end of the melt season but remain frozen over the winter. It is very difficult to estimate how much. In this experimental dataset we assume that it is 25% of the observed September water volume that is frozen and stored during winter.
4. Subglacial meltwater flux maps were computed Greenland-wide, and integrated over the drainage basins of interest to produce monthly estimates of basal runoff.
Please read the README_TotalRunOff.txt

本数据集涵盖2014年至2021年期间格陵兰岛五个流域（NEGIS、北方湖泊、南方湖泊、Store和Watson）的总月径流量，包括地表径流和基岩径流。径流量通过将地表融水、雪/冰层保留、冰川表面变化和冰川下径流相加，得到每月流域尺度的估计值。
1. 从选定的区域气候模型（RCM）中按月计算地表水体，通过将地表融水和液态降水（降雨）相加。
2. 通过从RCM径流中减去RCM地表融水，计算雪/冰层覆盖部分的冰层保留量。
3. 冰川表面变化体积的估算采用兰开斯特大学提出的方法论，通过RT算法在S2图像中划界冰川湖泊范围，并利用辐射传输模型（第2.2.6.1节技术文档）计算湖泊深度。湖泊深度通过Sentinel 2红色波段影像（波段4）确定。通过将每个单个湖泊多边形的湖泊深度与湖泊面积相乘，并对流域面积进行求和，计算出总湖泊体积。通过与ICESat-2横切面比较，确定体积不确定性。该不确定性表示为通过ICESat-2横切面集成的湖泊深度与相应由S2得出的湖泊深度横切面之间的最大百分比差异。对于红色波段，发现湖泊体积被低估了高达33.5%。
部分冰川湖泊中的融水在融雪季节结束时不会离开冰盖，而是会冻结过冬。很难估算其具体数量。在本实验数据集中，我们假设为观测到的9月份水体积的25%在冬季冻结并储存。
4. 计算了格陵兰岛全境的冰川下融水通量图，并对感兴趣的流域进行积分，以产生每月基岩径流的估计值。
请参阅README_TotalRunOff.txt