三类陆面模式模拟土壤湿度廓线的对比研究

针对不同陆面模式对土壤湿度方程求解方法以及对土壤分层结构的差异， 本文选取了三类陆面模式（CLM, CABLE和ECMWF陆面模式）作比较研究。为了避免不同模式参数化方案引起的上边界误差， 上边界采用固定蒸发率、 入渗率和固定表层土壤湿度三类边界条件。土壤分层采用101层（细网格）和11层（粗网格）两种， 并考虑土壤性质沿深度变化。结果表明： 当土壤性质均匀时， 求解的差别主要在第三类边界条件下CLM 求出的水分入渗速度比其它两种快； 改用粗网格后由于土壤深层厚度加大无法与细网格得出的土壤湿度廓线相重合。当土壤性质非均匀时， 模拟结果间差别加大， 只有ECMWF模式模拟的土壤湿度廓线是严格连续的。对于模式和上边界的不同组合， 粗、 细网格模拟结果间均方根偏差不一致。一般而言， CABLE模拟的偏差除第一类条件较小外， 其它都是最大的。第二三类边界条件引起的偏差较大， 第一类最小。上述结果提示我们, 在比较不同陆面模式以及用观测资料来检验模拟结果时应充分考虑土壤分层及土壤性质非均匀性的可能影响。

A Comparative Study of the Three Land Surface Models in Simulating the Soil Moisture Profile

Considering different finite-difference techniques and different numbers of soil layers used for solving the soil moisture equation among the different land surface models (LSMs), three land surface models are compared in the context of simulating the soil moisture profile under the three upper boundary conditions(BCs) (i.e., a fixed evaporation rate, a fixed infiltration rate and a fixed surface soil moisture) with a finely spaced grid with 101 layers and a coarser grid with 11 layers. Also the impact of soil textures are took into an account. The results show that if the soil along depth is homogeneous (i.e. one soil type with fixed percentages of sand, clay and loam), the main difference among the soil moisture profiles simulated with the three schemes is that the infiltration of soil water with the CLM is faster than that with the other two models, and with the decrease of soil layers from 101 to 11, the soil moisture profile especially at the last three layers is inconsistent with that simulated with the fine grid; if the soil along the depth is heterogeneous (i.e. still one soil type but with different percentages of sand, clay and loam in each of 101 layers), the difference of simulated soil moisture profiles is enlarged and only the soil moisture profile with the ECMWF LSM is continuous. With the change of LSMs and the upper BCs, the rms difference between the soil moistures simulated respectively with the fine and coarse grids is not consistent: The rms difference from the CABLE generally is the largest except with the first upper BC and the RMS with the second and third BCs is larger compared with the first BC. The results imply that the impact of the number of soil layers should be taken into account when we intercompare the different land models or compare the simulating results with the observations.