Data description

1. Clinical Disease Surveillance Data

The data was extracted from the California Department of Public Health weekly reports spanning 2003 to 2023, available at California West Nile Virus Reports. This dataset includes weekly reports of human cases from 2004 to the present for each county in California. The cases were extracted from individual PDF files.

Please note that the data may not align perfectly with the annual summaries published by the department. For higher accuracy, you can contact the California Department of Public Health directly to request official data.

To ensure data sensitivity, this webpage only displays data scraped from the publicly available weekly reports.

2. Climate data processing

For each data row representing a specific geographic location and year within our study, I employed the xarray library in Python to process the ERA5-Land monthly averaged climatic data , which covers the period from 1950 to the present.For the monthly report dataset, I extracted the monthly average values for each climate variable within the monthly on the corresponding county. To better understand the past climate variables effect. For comparison, the average monthly data of the previous one month, two months is also extracted for each location and climate variable.

Table 1: Description of Environmental Variables
Variable Name	Description
Population	The human population of the county based on the census from U.S. census Bureau.
Avian Phylodiversity	Derived from eBird data, this variable represents the diversity of bird species in a given area, weighted by their evolutionary relationships.
Average daylight hours	The average number of daylight hours over the month of each data point in the WNV dataset, influencing biological and environmental processes.
10m eastward wind	The eastward component of wind speed at 10 meters above the ground.
10m northward wind	The northward component of wind speed at 10 meters above the ground.
2m temperature	Air temperature measured at 2 meters above the ground.
Evaporation from bare soil	The amount of water evaporating directly from bare soil surfaces.
Leaf area index for high vegetation	One-half of the total green leaf area per unit horizontal ground surface area for high vegetation type.
Leaf area index for low vegetation	One-half of the total green leaf area per unit horizontal ground surface area for low vegetation type.
Water retention capacity of land	Amount of water in the vegetation canopy and/or in a thin layer on the soil.
Snowfall	The total amount of snow that falls over a specified period.
Surface net solar radiation	The net amount of solar radiation reaching the earth's surface.
Surface runoff	The amount of water that flows over the land surface after rainfall.
Total evaporation	The total amount of water evaporated from all sources, including soil and vegetation.
Total precipitation	Accumulated liquid and frozen water, including rain and snow, that falls to the Earth's surface.
Volumetric soil water layer 1	Volume of water in soil layer 1 (0 - 7 cm) of the ECMWF Integrated Forecasting System.
Evergreen/Deciduous Needleleaf Trees	A class of vegetation dominated by needleleaf trees, including both evergreen and deciduous species.
Evergreen Broadleaf Trees	A class of vegetation dominated by broadleaf trees that retain their leaves year-round.
Deciduous Broadleaf Trees	A class of vegetation dominated by broadleaf trees that lose their leaves seasonally.
Mixed/Other Trees	A combination of various tree types or other less dominant vegetation classes.
Shrubs	Low-growing woody plants with multiple stems.
Herbaceous Vegetation	Non-woody plants, such as grasses, ferns, and flowers.
Cultivated and Managed Vegetation	Areas dominated by human-managed vegetation, such as crops or orchards.
Regularly Flooded Vegetation	Vegetation that grows in areas regularly subjected to flooding.
Urban/Built-up	Areas dominated by human-made structures, such as cities and towns.
Snow/Ice	Areas covered by perennial snow or ice, such as glaciers.
Barren	Land with little to no vegetation, such as deserts or rocky areas.
Open Water	Areas covered by water, such as lakes, rivers, or oceans.