Spatial Variability of precipitation lapse rates incomplex topographical regions - application in France

The estimation of annual precipitation in ungauged mountainous areas where stations

are primarily situated in valleys is a crucial task in hydrology. Water Resources are very un-

certain at high altitudes due to difficult estimations of ice cover, water content in snowpacks,

and the weak instrumentation of these remote lands. Precipitation lapse rates (PLRs) are

defined as the increasing or decreasing rate of precipitation amounts with the elevation, and

play a pivotal role in this regard. However, the documentation of PLR in mountainous re-

gions remains weak even though their utilization in hydrological applications is5 important.

PLRs are often computed from rain gauge amounts, which are dependent on spatial sampling

and are not representative of high-altitude areas. The emergence and accessibility of gridded

precipitation products offer a remarkable opportunity to investigate the spatial variability

and the spatial-scale dependence of PLR in a varied and complex topography region. At the

regional scale (10,000 km2), six different rainfall products (rainfall reanalysis, satellite, radar)

are compared in their ability to reproduce the altitude dependence of the annual precipita-

tion of 1836 stations located in France. The Convection-Permitting Regional Climate Model

(CP-RCM) AROME is found to be more appropriate than radar and satellite-based products

commonly used in hydrology. The fine resolution of AROME (2.5 km) allows for a precise

assessment of the influence of the altitude on annual precipitation on 23 massifs (∼ 1000

km2) and 2748 small catchments (∼ 100 km2) through linear regressions. With AROME,

PLRs are in the majority positive (95 % in the range 0.55–13.10 %/100 m). The variabil-

ity of PLR is higher in high-altitude regions such as the French Alps, reflecting sheltering

effects. This study emphasizes the interest of conducting PLR investigation at a fine scale

to effectively assess their spatial variability and therefore reliable precipitation estimates in

mountainous areas, respecting the hydrological balance in high-altitude catchments.