Spatial water data and time series can be challenging to work with – you cannot just open them in a spreadsheet. The Global Water Monitor Data Explorer aims to save you the trouble and provide direct access to data through maps, accounts and charts. Data can be examined by point location or region, compared to preceding years, or downloaded for further analysis.
The Data Explorer currently offers data on precipitation, air temperature and humidity, soil water, river flows and water volumes in natural and artificial lakes.
Summarising by country or catchment
Summaries are calculated by country, broadly defined as regions recognised as independent or partially independent countries by the International Organisation for Standardization (ISO 3166-1). They include both fully independent countries and dependent administrative regions with a variable degree of autonomy. In the data explorer, summary data are also available for the next lower level of administrative regions (e.g., states and provinces) within each country provided by ISO. We imply no political views by using the current ISO list.
Many of the world’s river basins cover more than one country. In those cases, country statistics do not provide a complete picture of water resource conditions across the river basin. Conversely, large countries may contain multiple river basins, and their conditions can differ. Therefore, summaries were also calculated by river basin. In the case of islands and coastal regions with multiple small catchments, river ‘basins’ can be a series of bordering catchments. In the data explorer, summary data are also available for individual smaller catchments. Where there are no gaps in the climate and soil water data, averages across countries or catchments can be calculated without problems. Where there are some missing data, these can be estimated. However, where most data is missing, calculating averages based on the remaining data can be misleading.
Summarising storage in lakes and reservoirs by country or basin is straightforward in principle, as they can be added up. However, not all water bodies are measured all the time, so gaps in the data need to be based on estimates from other times. Summarising river flows by country or catchment can be more challenging. Most countries contain multiple rivers. We selected the fifteen river observation locations with the largest long-term average flows within the country or catchment. We subsequently calculated a weighted average value.
The ‘normal’ range of climate and water conditions varies worldwide, from arid deserts to tropical monsoon regions and frozen poles. Percentages and anomalies are valuable ways of comparing actual values to the distribution of values for the same area and time of year in the historical record. The following ways were used to calculate anomalies:
- Anomaly or absolute difference from mean provides information on the departure from long-term average conditions. For example, rainfall in a particular period (e.g., March to September) may be 100mm more than the average for the same period in all previous years.
- Percentage of the mean puts the same information in a relative context. For example, the same 100 mm difference would be 110% of (or 10% above) a longer-term average value of 1000 mm.
- Standardised anomaly or sigma value is a useful means to compare the actual conditions to previous years in a way that allows for the year-to-year variation experienced previously. It is calculated by dividing the actual anomaly by the standard deviation of values in previous years. Sigma values greater than 2 or less than -2 can be considered unusual and often coincide with extreme values in the available record, but not always.
Satellite instruments can provide a near-immediate global overview of climate and water conditions, but they are not perfect. Where they are available, onsite observations are usually more accurate and necessary to calibrate remote sensing approaches such as those used here. Protecting our remaining water measurement station network should be a priority.
Record length, frequency and spatial detail vary between data sources. For example, climate data are available from 1979 onwards, water body data from 1984 onwards, and soil water and river flow data are available from 2000 onwards. Also, measurements can be unavailable in some regions and at some times. For example, soil water observations are only possible if the soil is not frozen or covered with dense forest, and river flow observations require days without clouds.
By its very nature, averaging over years and regions can hide locally severe conditions or extreme conditions that occur over short periods. This should be kept in mind when interpreting the information.
The above limitations should be kept in mind. Anyone inclined to take action based on the information presented here should contact the relevant local or national agencies to confirm the information provided.