Enhancing streamflow forecast and extracting insights using long-short term memory networks with data integration at continental scales

TL;DR

This study demonstrates that integrating diverse recent observations using LSTM and CNN-based data integration significantly improves continental-scale streamflow forecasts, especially in high-flow regions, with insights into hydrologic process impacts.

Contribution

The paper introduces a flexible data integration procedure for LSTM models that leverages various recent discharge observations to enhance streamflow forecast accuracy at large scales.

Findings

DI improves forecast performance to a median NSE of 0.86.

Integration benefits are greatest in high-flow, autocorrelated regions.

Limitations remain for high-aridity basins with flash peaks.

Abstract

Recent observations with varied schedules and types (moving average, snapshot, or regularly spaced) can help to improve streamflow forecasts, but it is challenging to integrate them effectively. Based on a long short-term memory (LSTM) streamflow model, we tested multiple versions of a flexible procedure we call data integration (DI) to leverage recent discharge measurements to improve forecasts. DI accepts lagged inputs either directly or through a convolutional neural network (CNN) unit. DI ubiquitously elevated streamflow forecast performance to unseen levels, reaching a record continental-scale median Nash-Sutcliffe Efficiency coefficient value of 0.86. Integrating moving-average discharge, discharge from the last few days, or even average discharge from the previous calendar month could all improve daily forecasts. Directly using lagged observations as inputs was comparable in performance to using the CNN unit. Importantly, we obtained valuable insights regarding hydrologic processes impacting LSTM and DI performance. Before applying DI, the base LSTM model worked well in mountainous or snow-dominated regions, but less well in regions with low discharge volumes (due to either low precipitation or high precipitation-energy synchronicity) and large inter-annual storage variability. DI was most beneficial in regions with high flow autocorrelation: it greatly reduced baseflow bias in groundwater-dominated western basins and also improved peak prediction for basins with dynamical surface water storage, such as the Prairie Potholes or Great Lakes regions. However, even DI cannot elevate high-aridity basins with one-day flash peaks. Despite this limitation, there is much promise for a deep-learning-based forecast paradigm due to its performance, automation, efficiency, and flexibility.