Highlights from the Literature: July to September 2018

Oct 25, 2018

Data products distributed by the Land Processes (LP) Distributed Active Archive Center (DAAC) are used in many different Earth science applications. They play an important role in modeling, helping to detect changes to the landscape, and assessing ecosystem variables, to name a few. Three of those applications, published between July and September 2018, are highlighted below. A more comprehensive list is accessible on the LP DAAC Publications webpage.

Diem, P. K., Pimple, U., Sitthi, A., Varnakovida, P., Tanaka, K., Pungkul, S., Leadprathom, K., LeClerc, M., and Chidthaisong, A., 2018, Shifts in growing season of tropical deciduous forests as driven by El Niño and La Niña during 2001–2016: Forests, v. 9, no. 8, p. 448. at https://doi.org/10.3390/f9080448.

An understanding of how forests respond to extreme climate events is important to the development of adaptation strategies for forest conservation. This study focuses on how extreme climate events affected the timing and duration of the growing season of two tropical deciduous forest types in northern Thailand during El Niño and La Niña years. A combination of in-situ data, satellite-based vegetation metrics, and local climate variables are used to assess phenological changes in the study area from 2001 to 2016. The Normalized Difference Vegetation Index (NDVI) is used to derive information on the start of the growing season, end of the growing season, and length of the growing season, which are important indicators of vegetation response to climate changes. Diem and others (2018) calculate NDVI from the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) Surface Reflectance data product (MOD09Q1) using the red and near-infrared bands. Landsat 8 Operational Land Imager (OLI) data are also used to classify land cover types, and elevation values from the NASA Shuttle Radar Topography Mission (SRTM) version 3 digital elevation model (DEM) data product (SRTMGL1) are used to apply topographic corrections. The results of the study found that precipitation and temperature anomalies associated with El Niño and La Niña affected the response of phenological metrics in these tropical deciduous forests. The authors found a delay in the start of the growing season during El Niño, and contrarily, an advance to the start of the growing season during La Niña, which could potentially have an impact on forest health and the ecosystem services these forests provide. The authors note that tropical deciduous forests may become increasingly vulnerable if more frequent and intense extreme climate events occur; however, we have a chance to improve mitigation strategies to reduce risk of harm to forest health given a more thorough understanding of how these forests might respond.

Kolios, S., Mitrakos, S., and Stylios, C., 2018, Detection of areas susceptible to land degradation in Cyprus using remote sensed data and environmental quality indices: Land Degradation and Development, v. 29, no. 8, p. 2338–2350, at https://doi.org/10.1002/ldr.3024.

Land degradation is a major problem worldwide that has many consequences, including soil erosion, water pollution, and loss of soil structure. This study sought to detect areas in Cyprus that were vulnerable to land degradation between 2000 and 2016 using a combination of remotely sensed data and demographic information. Kolios and others (2018) calculate four quality indices (Climate Quality Index, Demographic Index, Soil Quality Index, and Vegetation Quality Index) before combining them into the Environmental Sensitivity Area Index (ESAI), which provides information on environmental risk of the land. The authors use the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Elevation Model Version 2 (ASTGTM) data product to calculate aspect, an input parameter to the Climate Quality Index. Other data are used to determine risk of land degradation, including Landsat and population density from the Gridded Population of the World data product. The results of the ESAI showed that 9.68 percent of Cyprus is at risk of land degradation, including around the Troodos Mountain, one of the most vegetated areas of the island. The authors note that the exclusive use of remotely sensed data products for this regional analysis was an innovative approach and was useful in providing essential information to determine environmental risk.

Nagy, A., Féher, J., and Tamás, J., 2018, Wheat and maize yield forecasting for the Tisza River catchment using MODIS NDVI time series and reported crop statistics: Computers and Electronics in Agriculture, v.151, p. 41–49, at https://doi.org/10.1016/j.compag.2018.05.035

Many studies have shown that satellite data are very useful in agricultural studies, such as providing information about crop type and health conditions. In this paper, Nagy and others (2018) focused on developing and testing an early season wheat and maize yield forecasting tool in the lowlands of the Tisza River catchment in Central Eastern Europe. The authors use a timeseries (2000–2015) of the Normalized Difference Vegetation Index (NDVI) layer from the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) Vegetation Indices data product (MOD13Q1) to map the locations of wheat and maize in the study area and to forecast yield. Elevation data from the NASA Shuttle Radar Topography Mission (SRTM) version 3 digital elevation model (DEM) data product (SRTMGL1) is also used to derive a crop mask along with CORINE (COoRdinate INformation on the Environment) Landcover datasets. The authors derive the yield forecasts using a simple linear regression analysis comparing NDVI values with officially reported wheat yield. The results showed an agreement between wheat yield derived from MODIS NDVI data and reported wheat yield. The authors concluded that the forecasting method developed in this study performed acceptable in predicting wheat and maize yields; however, it is less reliable in the case of extreme drought or extreme precipitation. The authors concluded that the forecasting method needs further development but confirmed the usefulness of remotely sensed data products in achieving this.

Material written by Sydney Neeley​¹

¹ Innovate!, Inc., contractor to the U.S. Geological Survey, Earth Resources Observation and Science (EROS) Center, Sioux Falls, South Dakota, USA. Work performed under USGS contract G15PC00012 for LP DAAC2.

² LP DAAC Work performed under NASA contract NNG14HH33I.