NCAR Community Land Model (CLM 2.0)

The Community Land Model is the land model for the Community Climate System Model (CCSM) and the Community Atmosphere Model (CAM). The current version of the Community Land Model is CLM 2.0. CLM 2.0 evolved from the NCAR LSM (LSM 1.0), BATS, and IAP94 land surface models as part of the development of the next versions of these climate models. CLM 2.0 is a collaborative project between scientists in the Terrestrial Sciences Section of the Climate and Global Dynamics Division (CGD) at the National Center for Atmospheric Research (NCAR) and the CCSM Land Model Working Group. Other principal working groups that also contribute to the CLM are Biogeochemistry, Paleoclimate, and Climate Change and Assessment.

The model formalizes and quantifies concepts of ecological climatology. Ecological climatology is an interdisciplinary framework to understand how natural and human changes in vegetation affect climate. It examines the physical, chemical, and biological processes by which terrestrial ecosystems affect and are affected by climate across a variety of spatial and temporal scales. The central theme is that terrestrial ecosystems, through their cycling of energy, water, chemical elements, and trace gases, are important determinants of climate.

The model has several components:

Biogeophysics -- This is the instantaneous exchanges of energy, water, and momentum with the atmosphere. It concerns aspects of micrometeorology, canopy physiology, soil physics, radiative transfer, and hydrology. Surface fluxes of energy, moisture, and momentum influence simulated surface climate.

Hydrologic cycle -- The hydrologic cycle over land includes interception of water by plant foliage and wood, throughfall and stemflow, infiltration, runoff, soil water, and snow. These are directly linked to the biogeophysics and also affect temperature, precipitation, and runoff. Total runoff (surface and sub-surface drainage) are routed downstream to oceans using a river routing model. Major global river systems are clearly evident in the model ouput.

Biogeochemistry -- This is the instantaneous exchanges of chemical constituents with the atmosphere. Current projects include: carbon, biogenic volatile organic compounds, dust, dry deposition.

Dynamic vegetation -- This includes the carbon cycle but also changes in community composition and vegetation structure in response to disturbance (e.g., fire, land use) and climate change. There are two time-scales for this dynamics: Succession considers changes in community composition and vegetation structure over periods up to several hundred years, typically following disturbance such as fire or land use. Over longer periods of times (e.g., centuries, millenia), the biogeography of vegetation changes in response to climate change. There are two main projects related to dynamic vegetation. Peter Thornton is leading an effort to add the carbon and nitrogen cycles to the Community Land Model. This uses carbon and nitrogen parameterizations of the BIOME-BGC model. Vegetation structure (e.g., leaf area index, carbon pools) changes over time, but community composition is prescribed. Gordon Bonan and Sam Levis are leading an effort to allow for dynamic community composition. The current implementation of dynamic vegetation uses many of ideas formulated in the Lund-Potsdam-Jena dynamic global vegetation model.

The land surface is represented by 5 primary sub-grid land cover types (glacier, lake, wetland, urban, vegetated) in each grid cell. The vegetated portion of a grid cell is further divided into patches of plant functional types, each with its own leaf and stem area index and canopy height. Each subgrid land cover type and PFT patch is a separate column for energy and water calculations.

CLM 2.0 currently includes biogeophysics and river routing. The biogeochemistry and dynamic vegetation modules are not yet released.

通用陆面模式（Community Land Model，CLM）是社区气候系统模型（Community Climate System Model，CCSM）与社区大气模式（Community Atmosphere Model，CAM）配套的陆面模式。当前通用陆面模式的正式版本为CLM 2.0。CLM 2.0衍生自美国国家大气研究中心（National Center for Atmospheric Research，NCAR）的LSM（LSM 1.0）、BATS以及IAP94三款陆面模式，是上述气候模型迭代开发的核心组成部分。CLM 2.0是由美国国家大气研究中心气候与全球动力学分部（Climate and Global Dynamics Division，CGD）陆地科学部的科研人员，与CCSM陆面模式工作组共同推进的合作研发项目。其他为CLM研发提供核心支撑的工作组还包括生物地球化学、古气候以及气候变化与评估工作组。

该模式对生态气候学的相关概念进行了形式化定义与量化表征。生态气候学是一门跨学科研究范式，旨在阐释自然与人为植被变化对气候的影响机制，其研究覆盖不同时空尺度下，陆地生态系统影响气候以及受气候扰动的物理、化学与生物过程。该领域的核心要义为：陆地生态系统通过能量、水、化学元素与痕量气体的循环过程，是气候形成与演变的重要驱动因子。

该模式包含以下核心模块：
- 生物地球物理学模块：负责实现陆地与大气之间能量、水与动量的瞬时交换，涵盖微气象学、冠层生理学、土壤物理学、辐射传输与水文学等研究方向。地表能量、水汽与动量通量会直接调控模拟的地表气候状态。
- 水文循环模块：陆地水文循环过程包含植物冠层与木质组织截水、穿透雨与茎流、入渗、径流、土壤水与积雪等关键环节。这些过程与生物地球物理学模块直接耦合，同时也会对区域温度、降水与径流特征产生显著影响。模式通过河道汇流模型将总径流（含地表与地下排水）向下游输送至海洋，模拟输出结果可清晰呈现全球主要河流水系的分布特征。
- 生物地球化学模块：负责实现陆地与大气之间化学组分的瞬时交换，当前研发方向包括碳循环、生物源挥发性有机化合物、沙尘与干沉降。
- 动态植被模块：该模块不仅涵盖碳循环过程，还包含陆地生态系统群落组成与植被结构在受干扰（如火灾、土地利用）与气候变化驱动下的动态变化。该动态过程包含两类时间尺度：演替过程关注火灾、土地利用等干扰事件发生后数百年尺度内的群落组成与植被结构演变；长周期生物地理变化则聚焦于百年至千年尺度上，植被生物地理学特征随气候变化产生的适应性改变。针对动态植被模块，目前有两项核心研发工作：其一由Peter Thornton主导，旨在为CLM集成碳与氮循环模块，该工作采用了BIOME-BGC模型的碳氮参数化方案，植被结构（如叶面积指数、碳库）可随时间动态变化，但群落组成采用预设参数；其二由Gordon Bonan与Sam Levis主导，目标是实现群落组成的动态模拟。当前动态植被模块的实现方案借鉴了伦德-波茨坦-耶拿动态全球植被模型（Lund-Potsdam-Jena dynamic global vegetation model）的诸多核心思路。

每个网格单元的陆面通过5类主要的次网格土地覆盖类型（冰川、湖泊、湿地、城市用地与植被覆盖）进行表征。其中植被覆盖区域还会进一步划分为不同的植物功能型（plant functional types，PFT）斑块，每个斑块拥有独立的叶面积指数、茎面积指数与冠层高度。每一类次网格土地覆盖类型与植物功能型斑块均作为独立的计算列，用于能量与水循环的数值模拟。

CLM 2.0当前已正式集成生物地球物理学模块与河道汇流模块，生物地球化学与动态植被模块尚未对外发布。