Recent updates

Several changes have been made to GCAM since the last release version (v4.4). The key updates are:

Water demands are now included (see Water Demand)
Land use regions are now based on water basins (see Land Regions)
Multiple agricultural management practices are included (see Agricultural Management)
The GCAM Shared Socioeconomic Pathways are included (see SSPs)
A newer version of Hector is included (see Hector)
Update to a new data system (see Data System)
Updated land use-land cover history (see Land History)
Model Interface bug fixes and support for Java 9/10.

The sections below provide short summaries of all changes.

Water Demand

GCAM5.1 represents demand for water by sector and technology, including both water withdrawals and water consumption.

Land Regions

GCAM5.1 switches land use regions from climatically defined agro-ecological zones (AEZs) developed by the GTAP group to water basin-defined geographic land units (GLUs), developed in house.

Agricultural Management

GCAM5.1 endogenizes yields and fertilizer application rates, making these levels each a function of crop prices, production costs, and other contributors to modeled land profit rates. This is achieved by nesting four different crop technologies within the logit structure (irrigated/hi fertilizer, irrigated/lo fertilizer, rainfed/hi fertilizer, rainfed/lo fertilizer).

SSPs

GCAM5.1 includes the ability to model five alternative Shared Socioeconomic Pathways, as described in Calvin et al. (2017).

Hector

GCAM5.1 includes Hector v2.0, which (1) adds a better representation of oceanic heat uptake, (2) simulates the temperature response from volcanic forcings in the historical period, and (3) addresses odd results found in the impulse response experiments.

Data System

GCAM converts the system for processing GCAM inputs into an R package using clean, consistent, well-documented code. The data system is available on github.

Land History

GCAM5.1 updates the land use and land cover history to use outputs from Moirai.