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Summary of CLM4.5 Development

The development of CLM4.5 was motivated by the need to incorporate recent scientific advances in understanding and representing land surface processes, expand model capabilities, and improve forcing datasets. Key updates include:

Canopy Processes
- Revised canopy radiation scheme and scaling of leaf processes
- Co-limitations on photosynthesis and temperature acclimation

Hydrology 
- Hydraulic properties of frozen soils based on liquid water content
- New snow cover fraction parameterization 
- Revised lake model

Biogeochemistry
- Vertically resolved soil biogeochemistry
- Updated litter/soil carbon-nitrogen pools and processes
- New fire model with natural/anthropogenic triggers and suppressions

Additions
- Methane production/oxidation/emissions model
- Interactive crop fertilization, organ pools, and irrigation
- Optional multilayer canopy and variable infiltration capacity runoff

Forcing Data
- Replaced default forcing dataset with higher-resolution CRUNCEP

CLM4.5 was released in 2013 alongside CESM1.2, incorporating numerous scientific advances to improve the representation of land surface processes and interactions.