EARTH2OBSERVE: GLOBAL EARTH OBSERVATION FOR INTEGRATED
WATER RESOURCE ASSESSMENT, NEW ZEALAND CASE STUDY.
J. Schellekens1, F. Sperna Weiland1, R. Westerhoff1,2, M. Werner1
1
Deltares, 2 GNS Science
Introduction
Increasing demands from economic sectors such as industry, agriculture, energy, tourism and domestic
use put great pressure on global water resources and this pressure may be further increased due to a
changing climate. Yet, availability and quality of water resources are still difficult to estimate in different
regions of the world and many countries lack basic information or observation and monitoring systems.
A consistent global reanalysis dataset of water resources - an optimized global dataset that integrates
available earth observations, in-situ datasets and global hydrological models comprising hydrological
and meteorological water cycle components - is currently lacking. While numerous global datasets and
relevant satellite observations are becoming available. The project eartH2Observe integrates available
global earth observations (EO), in-situ datasets and global models and is constructing a global open
source water resources re-analysis (WRR) dataset of significant length (approximately 40 yrs). Some
global datasets are tested for application on a catchment scale. In New Zealand, this application focuses
on evapotranspiration, rainfall recharge and water tables.
Method
As a first step, a unified forcing dataset was produced in such a way that it could be used to drive both
the global land surface and the hydrological models. The resulting adjusted WFDEI forcing comprises
the period between 1979 and 2012 and contains both three hourly time intervals and daily time intervals.
WFDEI is based on the ECMWF ERA-Interim reanalysis with a spatial resolution of 0.5 x 0.5 degree
corrected with gridded in-situ observations from the GPCP dataset. Each participating global modelling
system was ran with this meteorological dataset and produced a first version of reanalysis data
consisting of amongst others surface runoff, soil moisture, evaporation and river discharge. Together
these datasets constitute the first Water Resources Reanalysis (Tier 1). We used a total of ten largescale hydrological models and land-surface models with extended hydrological schemes (WaterGAP3,
HTESSEL-CaMA, LISFLOOD, PCR-GLOBWB, ORCHIDEE, W3RA, SURFEX-TRIP, JULES, HBVSIMREG and SWBM). To ensure uniform input and use of the data, the projects servers have been
configured to host the forcing data and also provide an interchange platform for the project using a
THREDDS data server. This server is also used to distribute the data to the rest of the world and
includes an interactive portal. The first runs have been used to estimate continental runoff into the
oceans using the ensemble. The resulting ensemble estimate of 51450 km 3/yr compares well with other
estimates but the large spread between the models emphasizes the need for multi model simulations
and further constraining of the models using remote sensing data.
At the same time, user requirements in the case study areas have been gathered and the applicability
of the WRR-1 in these areas is being investigated. The case studies are conducted together with local
end-users and stakeholders. Regions of interest cover multiple continents, a variety of hydrological,
climatological and governance conditions and differ in degree of data richness (e.g. the Mediterranean
and Baltic region, Ethiopia, Colombia, Australia, New Zealand and Bangladesh). In New Zealand, the
project collaborates with the SMART Aquifer Characterisation Programme and has discussed its results
to all regional councils through the Groundwater Forum. Via use of the first WRR products and feedback
in the next incarnations of the WRR the case studies are very important through demonstrating the
applicability of the WRR and validating the data products locally. The data is disseminated through an
open data portal to ensure increased availability of global water resources information on both regional
and global scale.
Results
First testing of the products in the Australian case study has shown that the forcing in this region
matched the local data rather well. In addition, a significant improvement in simulated discharge was
shown after using EO derived soil moisture in a data assimilation scheme in the global PCR-GLOBWB
model indication that the combination of earth observations and models may provide the most accurate
results. The first results of downscaling techniques applied to the global forcing to derive reference
evapotranspiration show very similar results compared to local obtained estimates and a 10x10km high
resolution reference potential evapotranspiration product has been made. In New Zealand, application
of the data to water table estimates using a fully coupled land surface model and groundwater model
are currently tested and preliminary results will be shown. Results of the discussions with regional
stakeholders will also be presented at this presentation.