# Evaluating the Drainage Density Characteristics on Climate and Drainage Area Using LiDAR Data
###### Abstract  
The purpose of this study is to identify the relationship between drainage density and climate, as represented by the climate aridity index, and to understand the relationship between drainage density and drainage area. A total of 121 study sites with low human impact, and a wide range of climate aridity index 0.3 (humid)-10.4 (arid), were selected based on the availability of light detection and ranging (LiDAR) data, producing a digital elevation model (DEM) with a spatial resolution of 1 m. A curvature-based method, incorporating both positive and negative curvature information, was used to extract the valley (drainage) network from the LiDAR-based DEMs. Drainage density and climate aridity index exhibited a monotonically increasing trend, contrary to the previous results that have shown a U-shaped relationship. This discrepancy was caused by the selection of watersheds with extensive human activity in the previous study. One-meter resolution DEM produced greater drainage density than the previous studies with a coarse spatial resolution of 30 m as small valleys are not detectable in low-resolution topography datasets. The discrepancy between the previous study and the current study results encouraged further investigation of the impact of the drainage area (watershed size). A negative correlation between drainage density and drainage area was reconfirmed, while a stronger decreasing trend was observed in arid regions than in humid regions. climate aridity index; drainage density; drainage area; valley network extraction; LiDAR data +
Footnote †: journal: Applied Sciences  
produce a higher peak flow and sediment load [31]. Spatial heterogeneity of drainage density also affects surface and subsurface runoff [32]. Various factors control drainage density, including climate, lithology, vegetation, and topography [33; 34; 10; 35]. The most crucial factor that controls the watershed topography is considered to be climate [36]. Arid regions show a large variability of drainage density compared to humid regions because of the seasonal variation of climate [37]. [PERSON] [33] identified a negative correlation between drainage density and precipitation effectiveness (_PE_) index, which is defined as the product of 10 and the summation of ratios between monthly average precipitation and evaporation in watersheds in arid regions in the south-western United States [38]. In contrast, [PERSON] [39] discovered a positive correlation between drainage density and _PE_ index for humid watersheds in Sri Lanka. The contrasting relationships between \(D_{d}\) and \(PE\) index found in an arid region [33] and in a humid region [39] were explained as a U-shaped relationship by combining the data from both studies [40; 41; 42]. The U-shaped relationship has been explained as the trade-off between the resistance force of vegetation and the erosion force of runoff [40; 41; 42]. Not only the climate but also the size of a drainage area (\(A\)) affects the drainage density [43]. The drainage area is a proxy of watershed properties [44]. The hydrologic phenomenon is correlated with physiographic properties, which include the size of the drainage area [45]. [PERSON] [46] utilized a power law relationship, \(D_{d}\,\propto\,A^{-0.337}\), to describe the relationship between drainage area and drainage density, which indicates that drainage density decreases with a drainage area. The value of the exponent in the power law relationship depends on environmental characteristics such as climate, vegetation, and geology [47; 48]. Since both watershed properties and climate control drainage density, the relationship between drainage area and drainage density may vary from humid to arid regions. Therefore, it is necessary to investigate the impact of long-term climate and drainage area on drainage density simultaneously. For an accurate assessment, this study utilizes high-resolution DEMs to extract drainage networks. The extracted drainage networks were used to examine the relationship between drainage density, climate, and drainage area.