If you want to study the Critical Zone of hillslopes, start from here

Recently a paper by Fan et al,  Hillslope Hydrology in Global Change Research and Earth System Modeling,  was published on  Water Resources Research, 85(3), 319–36. At the beginning I was thinking: "Hey, here it is another of those review papers which do not add anyhing to the existing literature".  This is not actually the case. The paper  is a very good introduction to many issues related to the Critical zone and its modelling and a source of relevant literature, of which I give an excerpt below.  The paper is open access and therefore you do not need any subscription to get it.

References

• Ajami, H., Khan, U., Tuteja, N., & Sharma, A. (2016). Development of a computationally efficient semi-distributed hydrologic modeling application for soil moisture, lateral flow and runoff simulation. Environmental Modelling and Software, 85(C), 319–331. http://doi.org/10.1016/j.envsoft.2016.09.002
• Anne Dudek Ronan, D. E. P. C. E. T. J. C. (2007). Field study and simulation of diurnal temperature effects on infiltration and variably saturated flow beneath an ephemeral stream, 1–17.
• Brantley, S. L., Lebedeva, M. I., Balashow, V. N., Singha, K., Sullivan, P. L., & Stinchcomb, G. (2017). Toward a conceptual model relating chemical reaction fronts to water flow paths in hills. Geomorphology, 277, 100–117. http://doi.org/10.1016/j.geomorph.2016.09.027
• Bui, O., Leoncini, X., Hal. (2019). Growth of a tree with allocations rules: Part 1 - Kinematics, 1–12.
• Chaney, N. W., van Huijgevoort, M. H. J., Shevliakova, E., Malyshev, S., Milly, P. C. D., Gauthier, P. P. G., & Sulman, B. N. (2018). Harnessing big data to rethink land heterogeneity in Earth system models. Hydrology and Earth System Sciences, 22(6), 3311–3330. http://doi.org/10.5194/hess-22-3311-2018
• Clark, M. P., Fan, Y., Lawrence, D. M., Adam, J. C., Bolster, D., Gochis, D. J., et al. (2015). Improving the representation of hydrologic processes in Earth System Models. Water Resources Research, 51(8), 5929–5956. http://doi.org/10.1002/2015WR017096
• Dearborn, K. D., & Danby, R. K. (2017). Aspect and slope influence plant community composition more than elevation across forest–tundra ecotones in subarctic Canada. Journal of Vegetation Science, 595–604. http://doi.org/10.1111/jvs.12521
• Elliot, P. E., & Cowell, C. M. (2015). Slope Aspect Mediates Fine Scale Tree Establishment Patterns at Upper Treeline during Wet and Dry Periods of the 20th Century. Artic, Antartic and Alpine Research, 1–13. http://doi.org/10.1657/AAAR0014-025
• Fan, Y., Clark, M., Lawrence, D. M., Swenson, S., Band, L. E., Brantley, S. L., et al. (2019). Hillslope Hydrology in Global Change Research and Earth System Modeling. Water Resources Research, 85(3), 319–36. http://doi.org/10.1029/2018WR023903
• Fan, Y., Miguez-Macho, G., Jobbagy, E. G., Jackson, R. B., & Otero-Casal, C. (2017). Hydrologic regulation of plant rooting depth. Pnas, 1–7. http://doi.org/10.1073/pnas.1712381114
• Fisher, R. A., Koven, C. D., Andreregg, W. R. L., Christoffersen, B. O., Dietze, M. C., Farrior, C., et al. (2017). Vegetation Demographics in Earth System Models: a review of progress and priorities. Global Change Biology, 1–74. http://doi.org/10.1111/ijlh.12426
• Hazenberg, P., Fang, Y., Broxton, P., Gochis, D., Niu, G. Y., Pelletier, J. D., et al. (2015). A hybrid-3D hillslope hydrological model for use in Earth system models. Water Resources Research, 51(10), 8218–8239. http://doi.org/10.1002/2014WR016842
• Hengl, T., Mendes de Jesus, J., Heuvelink, G. B. M., Ruiperez Gonzalez, M., Kilibarda, M., Blagotić, A., et al. (2017). SoilGrids250m: Global gridded soil information based on machine learning. PLoS ONE, 12(2), e0169748–40. http://doi.org/10.1371/journal.pone.0169748
• Krakauer, N. Y., Li, H., & Fan, Y. (2014). Groundwater flow across spatial scales: importance for climate modeling. Environ. Res. Lett., 9(3), 034003–8. http://doi.org/10.1088/1748-9326/9/3/034003
• Noe, S. M., & Giersch, C. (2004). A simple dynamic model of photosynthesis in oak leaves: coupling leaf conductance and photosynthetic carbon fixation by a variable intracellular CO2 pool. Functional Plant Biology, 31(12), 1195–19. http://doi.org/10.1071/FP03251
• Pelletier, J. D., Barron-Gafford, G., Gutierrez-Jurado, H., Hinckley, E. S., Istanbullioglu, E., McGuire, L. A., et al. (2017). Which way do you lean? Using slope aspect variations to understand Critical Zone processes and feedbacks 
• Earth Surface Processes and Landforms, 1133–1154. http://doi.org/10.1002/esp.4306
• Rempe, D. M., & Dietrich, W. E. (2018). Direct observations of rock moisture, a hidden component of the hydrologic cycle. Proceedings of the National Academy of Sciences, 115(11), 2664–2669. http://doi.org/10.1073/pnas.1800141115
• Riebe, C. S., Hahm, W. J., & Brantley, S. L. (2017). ESD Reviews: Thermodynamic optimality in Earth sciences. The missing constraints in modeling Earth system dynamics? Earth Surface Processes and Landforms, 42, 128–156. http://doi.org/10.1002/esp.4052
• Schaller, M. F., & Fan, Y. (2009). River basins as groundwater exporters and importers: Implications for water cycle and climate modeling. Journal of Geophysical Research, 114(D4), D07103–21. http://doi.org/10.1029/2008JD010636
• Sullivan, P. L., Price, R. M., Ross, M. S., Stoffella, S. L., Sah, J. P., Scinto, L. J., et al. (2016). Trees: a powerful geomorphic agent governing the landscape evolution of a subtropical wetland. Biogeochemistry, 128(3), 369–384. http://doi.org/10.1007/s10533-016-0213-9
• Tesfa, T. K., Tarboton, D. G., Chandler, D. G., & McNamara, J. P. (2009). Modeling soil depth from topographic and land cover attributes. Water Resources Research, 45(10), 103–17. http://doi.org/10.1029/2008WR007474
• Westhoff, M., Kleidon, A., Schymanski, S., Dewals, B., Nijisse, F., Renner, M., et al. (2019). ESD Reviews: Thermodynamic optimality in Earth sciences. The missing constraints in modeling Earth system dynamics? 
• , 1–31. http://doi.org/10.5194/esd-2019-6
• Winter, T. C., Harvey, J. W., Franke, O. L., & Alley, W. M. (1998). Ground Water and Surface Water. U.S. Geological Survey Circular (Vol. 1139, pp. 1–87).
• Worthington, S. R. H., Davies, G. J., & E, C. A. (2016). Enhancement of bedrock permeability by weathering. Earth-Science Reviews, 160, 1–73. http://doi.org/10.1016/j.earscirev.2016.07.002
• Xu, X., & Liu, W. (2017). The global distribution of Earth's critical zone and its controlling factors. Geophysical Research Letters, 44(7), 3201–3208. http://doi.org/10.1002/2017GL072760
• Yamazaki, D., Ikeshima, D., Tawatari, R., Yamaguchi, T., O'Loughlin, F., Neal, J. C., et al. (2017). A high-accuracy map of global terrain elevations. Geophysical Research Letters, 44(11), 5844–5853. http://doi.org/10.1002/2017GL072874