# Tracking Dynamic Northern Surface Water Changes with High-Frequency Planet CubeSat Imagery
## 5 Discussion
### River-Foodplain Connectivity of the Yukon Flats  
The high spatial and temporal resolution of Planet imagery, accompanied by the non-binary classification method's ability to detect water extent in the variable quality data make Planet imagery particularly useful for study of complex, dynamic surface water systems. Floodplains and wetland environments are dependent on hydrologic recharge from rivers, precipitation and groundwater flow. However, the relationship between floodplain inundation and changes in main stem discharge is not well understood due to the complexity of flow patterns and limited in situ observations of large wetland regions [8; 52]. In high latitude wetlands such as the Yukon Flats, permafrost can further complicate these patterns by acting as a barrier between the surface and groundwater systems [13; 19; 20; 53; 54]. While the summer 2016 Planet acquisitions lack sufficient temporal sampling to fully address these questions, the observed patterns nonetheless enable general characterization of floodplain connectivity across our Yukon Flats study area (Figures 8 and 9). Figure 10: Normalized distribution of (**a**) top of atmosphere near infrared reflectance and (**b**) NDWI for Yukon Flats water bodies and surrounding vegetation in five different PlanetScope images. In the near infrared (**a**), water pixels are the left peak (lower band values) and in the NDWI (**b**), the second peak represents water pixels. The divergent and spatially variable changes in lake surface area observed between 23 June and 17 August (Figure 7) suggest that surface water extent in the Yukon Flats is driven by a combination of the seasonal runoff cycle (i.e., spring snowmelt flooding and recharge, followed by summer drying), connections with the Yukon River main-stem, localized topography/bathymetry [40] and substrate conditions (i.e., permafrost, geology). Previous analyses of hydrologic connectivity in other floodplain systems may help explain these patterns. While conceptual models commonly assume floodplains to have a uniform \"bathtub\" response to changing main-stem river stage, floodplain inundation is complex, driven by distributary channels, floodplain topography and storage in wetlands and lakes [52; 55]. In their analysis of the relationship between lake levels and inundation extent in the Peace Athabaska Delta, [PERSON] and [PERSON] (2008) find that water levels in the floodplain do not reflect water levels in the river. They observe a dichotomy between the distributary channel network and the surrounding lakes and wetlands wherein channels within the network respond to changes in river level but summertime peak flow events have little impact on the lakes and wetlands. In contrast, [PERSON] et al. (2005) present a diffusion model to explain how distance from the river channel controls the response of floodplain water levels to changes in main-stem river stage. Our findings do not support either a dichotomy between channel network and wetlands or a diffusion model; instead we observe larger scale variability wherein roughly one quarter of lakes respond to changes in river level, one half drain over the course of the season and one quarter are stable. The spatial patterns of this variability do not reveal any clear drivers of lake behavior (Figure 10). While a few lakes which respond strongly to August high stage events are clearly connected to the river system, in general there is no mechanism distinguishable in the imagery able to explain these differences. In their analysis of a flood-wave event in the Amazon basin, [PERSON] et al. (2007) observe a complex pattern of temporal changes in water level wherein variations in water height can be highly localized and the flow path cannot be predicted directly from bathymetry alone. Our observed patterns perhaps fit better with this result, where the spatiotemporal complexity of floodplain connectivity impedes characterizing or predicting individual lake response through a model or conceptual framework.