1. THE GCIP PROJECT

The Global Energy and Water Cycle Experiment (GEWEX) Continental-scale International Project (GCIP) was established to improve scientific understanding and to model on a continental scale the coupling between the atmosphere and the land surface for climate prediction purposes. Predicting variations in the earth's climate requires improved understanding of interaction between the atmosphere and land surface. Generally, the sensitivity of the earth's climate is determined by the energetic processes of the "fast climate system". The fast climate processes are manifested by clouds, insolation, precipitation, soil characteristics (moisture), vegetation, state of water resources, and the coupling processes between land surface moisture in (1) the partitioning of energy flux between latent and sensible heat, (2) interpreting precipitation variability; and (3) providing knowledge on infiltration and runoff, and its impact on energy and water budgets. The GCIP activities are focused on the Mississippi River basin (see Figure 1-1) to take advantage of the existing meteorological and hydrological networks that are being upgraded with new Doppler radars, wind profilers, and automatic weather stations. The operational or enhanced observing period (EOP) of GCIP began in October 1995 and is planned to continue for five years.

Figure 1-1 The Mississippi River basin, the focus of GCIP activities.

The GCIP Science Plan (WMO 1992) poses four principal questions that need to be addressed in order to advance the scientific research community's knowledge of the hydrological and energy cycles involved in the complex interactions between land, atmosphere, and ocean for a major river basin. These are:

• How do water and energy budgets vary in time and space on a continental scale?

• How can surface and groundwater processes at the catchment scale be aggregated interactively with the subgrid scale atmospheric processes in atmospheric models?

• How can the diverse measurements fundamental to the determination of hydrological and energy cycles be best incorporated (retrieved and assimilated) into analyses and coupled hydrologic-atmospheric models in a consistent fashion?

• What are the best approaches for assessing the effects of climate variability and change on water resources?

To address these four principal questions and others detailed in the GCIP Science Plan, the following objectives have been defined:

The long-term objective of GCIP is:

"To demonstrate skill in predicting changes in water resources on time scales up to seasonal, annual, and interannual as an integral part of the climate prediction system."

A rewriting of the GCIP Objectives by the NAS/NRC Gewex Panel in 1996 contributed to more focus of the GCIP research activities and near-term plans (IGPO 1996a):

1) Determine and explain the annual, interannual and spatial variability of the water and energy cycles within the Mississippi River basin.

2) Develop and evaluate coupled hydrologic/atmospheric models at resolutions appropriate to large-scale continental basins.

3) Develop and evaluate atmospheric, land, and coupled data assimilation schemes that incorporate both remote and in-situ observations.

4) Improve the utility of hydrologic predictions for water resources management up to seasonal and interannual time scales.

5) Provide access to comprehensive in-situ, remote sensing and model output data sets for use in GCIP research and as a benchmark for future studies.

The GCIP Implementation Plan, comprising three volumes, was completed in 1993 and 1994. Volume I of the GCIP Implementation Plan (IGPO 1993) is the overall planning document for the Project. It addresses the organizational framework for GCIP, the observational and database needs, and the upgrades to be made to existing operational analysis and prediction streams that produce routine four-dimensional data assimilation (4DDA) analyses for the GCIP and global domains. Volume II ( IGPO 1994a) examines the elements of a GCIP research program needed to assist the research community in addressing the specific scientific questions in the GCIP Science Plan. The overall plans for data management through the duration of the GCIP Project are described in Volume III of the GCIP Implementation Plan (IGPO 1994b).

GCIP is making use of existing operational and research programs to meet the research objectives. An important example is the U.S. Department of Energy, Atmospheric Radiation Measurement (ARM) Program, whose data from the Clouds and Radiation Testbed (CART) site are being made available to the GCIP effort. Opportunities for cooperation are being exploited with projects being formulated under other streams related to World Climate Research Programme (WCRP), such as the Climate Variations (CLIVAR) and the Global Ocean Atmosphere Land Surface (GOALS) Program. For example, the Pan American Climate Studies (PACS) project is being formed as a U.S. contribution to CLIVAR/GOALS to conduct research on the role of large-scale forcing from the tropics on continental precipitation in the Americas. A more complete description of collaborative research activities is given in Section 8.

1.3.1 Research Approach

GCIP research involves a systematic multiscale approach to accommodate physical process studies, model development, data assimilation, diagnostics, and validation topics. Such a multiscale developmental framework for the GCIP effort has three attributes:

(1) Support for a hierarchy of scales for observational work, algorithm and model development, and validation and diagnostic studies leading to a continental-scale capability.

(2) Capacity for sequential expansion to support the evolution of research themes (e.g., initial emphasis on hydrological implications of warm-season convective precipitation, moving next to issues related to midlatitude cold-season hydrology).

(3) Flexibility to develop methods and algorithms that can be applied in data-sparse areas of the globe outside the Mississippi River basin.

The understanding and modeling of a continental scale require, from the outset, consideration of nonlinear-scale interactions in the aggregation of smaller processes to the larger scale and vice versa. Progress in this area requires that methodologies be developed to represent the coupling of processes that are important in one medium (e.g., the atmosphere) to those that are important in another (e.g., the land surface). These techniques must be suitable at the resolution of operational prediction and general circulation models (GCM) (about 10 to 100 km) and hence must be capable of representing in aggregate the effects of high levels of heterogeneity in the underlying ground surface (WMO 1992). Accordingly, the GCIP research approach addresses activities on four scales (IGPO 1994a):

Continental-scale area (CSA) activities that span the entire domain of the Mississippi River basin with a scale size of about 3.2 x 10⁶ km².

Large-scale area (LSA) activities that occur in a phased timetable and emphasize a particular region with special characteristics for a period of about two years. Scale size is about 10⁵ to 10⁶ km². Four LSAs have been identified that in aggregate cover most of the GCIP domain, as shown in Figure 1- 2. The time phasing of activities within each of these areas is also shown in the figure.

Intermediate-scale area (ISA) activities that will be phased in with those for the LSAs and will serve as the basis for the regionalization of the parameters and coefficients of land surface hydrological models. Scale size is about 10³ to 10⁴ km².

Small-scale area (SSA) activities that typically occur in association with efforts requiring intensive observing periods (IOP) over a concentrated region to study a focused set of issues. Scale size is less than 10² km².

Figure 1-2 Boundaries for LSAs and temporal emphasis for each LSA from 1994 through 2000.

To the extent possible, the SSAs are being collocated with existing research basins, for example, the Little Washita Experimental Watershed in Oklahoma operated by the U.S. Department of Agriculture. The analyses, diagnostic studies, and model development on the SSA scale are being derived from operational data sources (augmented as necessary), existing research instrument complexes, and specially designed field programs of limited duration.

1.3.2 Continental Domain Synthesis

A fundamental thrust of the GCIP implementation strategy is that although the developmental activities are being initiated in limited regions, they lead toward an integrated continental-scale capability. Full continental domain studies have been important in GCIP from the beginning of the EOP in 1995. Retrospective analyses and baseline studies of water and energy balance have been the main focus of the research activities. In fact, as the EOP proceeds, the GCIP-derived budgets based on regional mesoscale models are superior in accuracy to budget estimates from other sources. These diagnostic studies will also be valuable for validating hydrological aspects of climate model simulations and understanding planetary-scale influences on North American hydrology.

1.4 Accomplishments to Date

The completion of the GCIP Science Plan in early 1992 heralded the beginning of a number of major activities in GCIP that have progressed steadily over the past five years. Some of the key accomplishments during this period are summarized in the remainder of this section within the scientific/technical implementation framework as outlined in the following section.

1.4.1 Scientific/Technical Implementation Framework

The two pivotal components of GCIP are (1) the development of a comprehensive observational database for the Mississippi River basin that will be available for GCIP analyses, and (2) the establishment of an evolving program of model development that will permit the observations to be extended spatially within GCIP or applied globally with new observations. A series of planned and ad hoc research and technical activities addressing observing systems, algorithm development, quality assurance issues, and water and energy budget studies link these pivotal components, as shown in Figure 1-3 (WMO 1992).

Figure 1-3 Strategy framework for implementing GCIP.

The GCIP research activities got underway in 1993 with primary support from NOAA. The results of these early research studies in data analysis, model development, diagnostics of model output, and observing system enhancements were published in a special issue of the Journal of Geophysical Research Volume 101, Number D3, March 20, 1996.

1.4.2 Research Path Achievements

During the past two years the research emphasis has been on warm season processes using data from the Arkansas-Red River basin in the southwestern part of the Mississippi river basin. Cold season processes using data from the Upper Mississippi River basin are being added. More than 100 papers have already been published in scientific journals. These research activities, although initiated in limited regions, are leading toward an integrated continental-scale capability.

1.4.3 Achievements in the Operational Centers

Since the approaches being taken by the principal operational analysis centers (e.g., the U.S. National Centers for Environmental Prediction [NCEP], the Canadian Meteorological Centre [CMC] and the ECMWF) are different, it is important that GCIP researchers have access to data from more than one assimilation scheme. The NCEP Eta Model and the NOAA Forecast Systems Laboratory MAPS Model are both high resolution nested regional models, the ECMWF and NCEP operate global models at coarser resolution while the CMC uses a variable grid approach with the Global Environmental Multiscale (GEM) Model . Further details on the achievements and near-term plans for improvements to the regional models are given in Section 2. The regional model output data are being made available to GCIP researchers with special efforts being made to archive the output from the regional mesoscale at a central location as described in Appendix B.

1.4.4 Database Development

The GCIP Science Plan (WMO 1992) recognized that the building of a database for GCIP scientists would be a major undertaking and that the amount and different types of data needed for GCIP studies would require an efficient data collection and management strategy.

The accomplishments to date in database development are in the areas of Pre-EOP data collection, compilation of several initial data sets, and the implementation of a distributed data management and service system.

1.4.5 Data Management and Service System

The responsibilities of the GCIP Data Management and Service System (DMSS) are to provide data services to GCIP investigators, adapt to the evolving data requirements, and compile the information on a five-year consolidated data set at the completion of the EOP. Carrying out these responsibilities involves an implementation approach with evolutionary improvements during the different stages of GCIP. The DMSS implementation strategy makes maximum use of existing data centers to minimize the lead time and expense required for development. These existing data centers are made an integral part of the GCIP-DMSS through four data source modules that specialize by data types (i.e., in situ, model output, satellite remote sensing, and GCIP special data) The primary responsibilities for the data source modules along with their major functions and activities were described in Volume III of the GCIP Implementation Plan (IGPO 1994b). Further details on data collection and management are given in Section 9.

1.5 Role and Structure of GCIP Major Activities Plan

The purpose of the Major Activities Plan is to project a description of GCIP research and associated activities over the next two to three years to preclude the need for frequent revisions to the three volumes of the GCIP Implementation Plan. The initial version of the Major Activities Plan covered the two-year period of 1995 and 1996 with an outlook for 1997 (IGPO 1994c) and was updated in each of the last two years (IGPO 1995; IGPO 1996a).

The description of planned activities is based on what should be done in an orderly progression toward the end objectives of GCIP and with a realistic assumption about the resources that will be available to do it. Adjustments are made the following year, as appropriate, to rationalize the plans with the actual resources. The adjustments are used as a starting point for projections in the following year's update.

This update of the Major Activities Plan covers the water years of 1998, 1999 and outlook for 2000. It was shown in Figure 1-2 that during this period there will be an emphasis on the four LSAs for two or more years. . Since activities are planned for each of the four LSAs, this will spread out the descriptions pertaining to specific objectives. Activities focused on the four science objectives are described in Sections 2 to 5. A number of variables were deemed critical to the success of GCIP and were designated as Principal Research Areas for GCIP. These include precipitation, soil moisture, land surface characteristics, and, clouds and radiation. The research activities for each of these critical variables are described in section 6. A summary of the research activities planned for each of the four LSAs and the CSA is given in section 7. The increasing importance of the collaborative research activities is described in section 8. The activities related to the data management objective are described in Sections 9 and 10 of this Plan.

1.6 GCIP after the Year 2000

The implementation planning for GCIP extends through the year 2000, as noted in Figure 1-2. A major phase of GCIP is the five-year Enhanced Observing Period that started on 1 October 1995 and is scheduled to be completed on 30 September 2000. This initiative is providing a comprehensive observational and model output database needed for GCIP research and as a benchmark for future studies.

GCIP has made tremendous strides in several of its science objectives during the past five years while others, such as the water resources objective, have not yet started. In addition a number of areas have evolved or started since the Implementation Plan was written in 1993 and 1994. Among those which could most affect GCIP plans after the year 2000 are:

1) GCIP and the Pan American Climate Studies(PACS) projects recently developed a prospectus as an initial step toward an integrated study of warm season predictability of precipitation and temperature over North America. It is predicated on the hypothesis that there is a deterministic element in the year-to-year variability of summertime precipitation and temperature over North America. The GCIP/PACS studies will address three major objectives:

i. Describe, explain and model the North American summer climate regime and its associated hydrologic cycle in the context of the evolving land surface-atmosphere-ocean annual cycle.

ii. Describe, explain and model North American warm season precipitation and temperature variability with emphasis on seasonal and interannual time scales.

iii. Describe, explain and model the spatial variability of summertime precipitation over North America on mesoscale to continental scale.

2) The CLIVAR Implementation Plan identifies GEWEX as the primary source of analyses and modeling of land surface processes as a contribution to global climate modeling. It is clear that the five Continental Scale Experiments (BALTEX, GAME, GCIP, LBA and MAGS), as part of the Gewex Hydrometeorology Panel, will need to play a strong role in this GEWEX contribution to CLIVAR. GCIP needs to develop its strategy for contributing to the overall program for the GEWEX Hydrometeorological Panel. In addition to the GEWEX contribution to CLIVAR, the Gewex Hydrometeorology Panel has set its own strategic objective:

By the year 2005 predict changes in water resources and soil moisture on time scales of seasonal to annual as an element of the World Climate Research Program's goals for the climate system.

3) The results of the research during the past five years, especially the successes with the mesoscale NWP models show that GCIP can now increase the time scale for predictions and should focus on developing an initial version of a coupled hydrologic/atmospheric climate model. Also, GCIP needs to increase the priority of its efforts in water resources applications to provide a contribution to the strategic objective for the GEWEX Hydrometeorology Panel.

It can be seen from the brief summary given above that the environment for GCIP research has changed significantly over the past five years since the GCIP Implementation Plan was written. Some changes were foreseen while others were not and the Preface to Volume I (IGPO 1993) states -- " These volumes of the implementation plan will evolve during the course of the project and each will be updated as required". It is apparent that some form of updating should be done to accommodate the knowledge gained during the past five years. It is considered that GCIP could benefit most from the updating of Volume II - RESEARCH- portion of the GCIP Implementation Plan. A proposal for a post-2000 implementation strategy as a first step in this process is given in Appendix A. It is also intended to provide a framework for updating the GCIP Major Activities Plan for the period 1998, 1999 and Outlook for 2000.