diff --git a/README.md b/README.md
index 08278a7..d30ab37 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@ pip install -r requirements.txt
 ```
 
 ### B. Data Download
-Download the GAUSS data from Globus (requires around 140GB of disk space):
+Download the GAUSS data from Globus (requires up to 140GB of disk space if all data is downloaded):
 1. First install the [Globus CLI](https://docs.globus.org/cli/):
     ```bash
     pip install globus-cli
@@ -39,10 +39,16 @@ Download the GAUSS data from Globus (requires around 140GB of disk space):
     ```bash
     globus login
     ```
-3. Download the data:
+3. Download the data. You can download all data (~140GB) using:
     ```bash
     sh scripts/download_gauss.sh 2e01e83a-5180-47f7-a6ab-c98b626ad9e4 <YOUR ENDPOINT ID> data/gauss/
     ```
+    
+    Or you can select a subset of the data to download (e.g. `tas` and `monthly`) using:
+    ```bash
+    sh scripts/download_gauss.sh 2e01e83a-5180-47f7-a6ab-c98b626ad9e4 <YOUR ENDPOINT ID> data/gauss/ --tas --monthly
+    ```
+    If only a subset of the data is downloaded, it will affect which of the following steps can successfully run. To fit the regression models, the monthly temperature (--tas --monthly) data must be downloaded at a minimum. At this time, it is only possible to subselect temperature (--tas) or precipitation (--pr) data.
 
 ### C. Data Processing
 1. Process the daily data to create monthly values. You can process all the daily data (both `tas` and `pr`) using:
diff --git a/scripts/download_gauss.sh b/scripts/download_gauss.sh
old mode 100644
new mode 100755
index 688e926..92a61bb
--- a/scripts/download_gauss.sh
+++ b/scripts/download_gauss.sh
@@ -1,6 +1,6 @@
 # Argument validation check
-if [ "$#" -ne 3 ]; then
-    echo "Usage: $0 <source_endpoint_id> <destination_endpoint_id> <local_destination>"
+if [ "$#" -lt 3 ] || [ "$#" -gt 5 ]; then
+    echo "Usage: $0 <source_endpoint_id> <destination_endpoint_id> <local_destination> [--tas | --pr] [--daily | --monthly]"
     exit 1
 fi
 
@@ -9,6 +9,51 @@ source_endpoint_id=$1
 destination_endpoint_id=$2
 local_destination=$3
 
+# Initialize optional variables
+download_tas=false
+download_pr=false
+download_daily=false
+download_monthly=false
+
+# Check for variable flags
+for arg in "${@:4}"
+do
+    case $arg in
+        --tas)
+            if [ "$download_pr" = true ]; then
+                echo "Error: You cannot select both ---tas and --pr."
+                exit 1
+            fi
+            download_tas=true
+        ;;
+        --pr)
+            if [ "$download_tas" = true ]; then
+                echo "Error: You cannot select both --tas and --pr."
+                exit 1
+            fi
+            download_pr=true
+        ;;
+        --daily)
+            if [ "$download_monthly" = true ]; then  
+                echo "Error: You cannot select both --daily and --monthly."
+                exit 1
+            fi
+            download_daily=true
+        ;;
+        --monthly)
+            if [ "$download_daily" = true ]; then
+                echo "Error: You cannot select both --daily and --monthly."
+                exit 1
+            fi
+            download_monthly=true
+        ;;
+        *)
+            echo "Invalid option: $arg"
+            exit 1
+            ;;
+    esac
+done
+
 # Create the local destination directory if it does not exist
 mkdir -p $local_destination
 
@@ -23,85 +68,121 @@ do
     base_dirs+=("/SSP245-MA-GAUSS-LOWER-1.0.00$i/atm/proc/tseries/month_1")
 done
 
-# Loop through each base directory and download the files
-for dir in "${base_dirs[@]}"
-do
-    echo "Listing files in $dir..."
-    # List files in the directory and filter for specific patterns
-    files=$(globus ls $source_endpoint_id:$dir | grep -E "\.TREFHT\.|\.\PRECT\.|\.TREFHTMN\.|\.TREFHTMX\.|\.QFLX\." | grep -E "\.h0\.")
+# Download monthly files as long as user disn't request just daily
+if [ "$download_daily" = false ]; then
+    # Define the file pattern based on the user's selection
+    file_pattern=""
+    if [ "$download_tas" = true ]; then
+        file_pattern="\.TREFHT\."
+    fi
+    if [ "$download_pr" = true ]; then
+        file_pattern="\.\PRECT\."
+    fi
+    if [ "$download_tas" = false ] && [ "$download_pr" = false ]; then
+        file_pattern="\.TREFHT\.|\.\PRECT\.|\.TREFHTMN\.|\.TREFHTMX\.|\.QFLX\."
+    fi
 
-    # Loop through filtered files and initiate transfer
-    for file in $files
+    # Loop through each base directory and download the files
+    for dir in "${base_dirs[@]}"
     do
-        # Check if file already exists at destination
-        if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
-            echo "Skipping $file, already exists at destination."
-        else
-            echo "Transferring $file from $dir..."
-            globus transfer $source_endpoint_id:$dir/$file $destination_endpoint_id:$local_destination$file
-        fi
-    done
-done
+        echo "Listing files in $dir... with file pattern $file_pattern"
+        # List files in the directory and filter for specific patterns
+        files=$(globus ls $source_endpoint_id:$dir | grep -E "$file_pattern" | grep -E "\.h0\.")
 
-# For MA-BASELINE.002 and MA-BASELINE.003, have to download PRECC and PRECL instead of PRECT
-for i in {2..3}
-do
-    echo "Listing files in /MA-BASELINE.00$i/atm/proc/tseries/month_1..."
-    files=$(globus ls $source_endpoint_id:/MA-BASELINE.00$i/atm/proc/tseries/month_1 | grep -E "\.PRECL\.|\.\PRECC\." | grep -E "\.h0\.")
-    for file in $files
-    do
-        if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
-            echo "Skipping $file, already exists at destination."
-        else
-            echo "Transferring $file from /MA-BASELINE.00$i/atm/proc/tseries/month_1..."
-            globus transfer $source_endpoint_id:/MA-BASELINE.00$i/atm/proc/tseries/month_1/$file $destination_endpoint_id:$local_destination$file
-        fi
+        # Loop through filtered files and initiate transfer
+        for file in $files
+        do
+            # Check if file already exists at destination
+            if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
+                echo "Skipping $file, already exists at destination."
+            else
+                echo "Transferring $file from $dir..."
+                globus transfer $source_endpoint_id:$dir/$file $destination_endpoint_id:$local_destination$file
+            fi
+        done
     done
-done
 
-# For MA-HISTORICAL, have to download PRECC and PRECL insrtead of PRECT
-for i in {1..3}
-do
-    echo "Listing files in /MA-HISTORICAL.00$i/atm/proc/tseries/month_1..."
-    files=$(globus ls $source_endpoint_id:/MA-HISTORICAL.00$i/atm/proc/tseries/month_1 | grep -E "\.PRECL\.|\.\PRECC\." | grep -E "\.h0\.")
-    for file in $files
-    do
-        if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
-            echo "Skipping $file, already exists at destination."
-        else
-            echo "Transferring $file from /MA-HISTORICAL.00$i/atm/proc/tseries/month_1..."
-            globus transfer $source_endpoint_id:/MA-HISTORICAL.00$i/atm/proc/tseries/month_1/$file $destination_endpoint_id:$local_destination$file
-        fi
-    done
-done
+    # Only download additional variables if not only downloading tas
+    if [ "$download_tas" = false ]; then
+        # For MA-BASELINE.002 and MA-BASELINE.003, have to download PRECC and PRECL instead of PRECT
+        for i in {2..3}
+        do
+            echo "Listing files in /MA-BASELINE.00$i/atm/proc/tseries/month_1... with file pattern \.PRECL\.|\.\PRECC\."
+            files=$(globus ls $source_endpoint_id:/MA-BASELINE.00$i/atm/proc/tseries/month_1 | grep -E "\.PRECL\.|\.\PRECC\." | grep -E "\.h0\.")
+            for file in $files
+            do
+                if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
+                    echo "Skipping $file, already exists at destination."
+                else
+                    echo "Transferring $file from /MA-BASELINE.00$i/atm/proc/tseries/month_1..."
+                    globus transfer $source_endpoint_id:/MA-BASELINE.00$i/atm/proc/tseries/month_1/$file $destination_endpoint_id:$local_destination$file
+                fi
+            done
+        done
 
-# Download daily TREFHT and PRECT files for base_dirs
-for dir in "${base_dirs[@]}"
-do
-    # Replace month with day
-    dir=$(echo $dir | sed 's/month_1/day_1/g')
-    echo "Listing files in $dir..."
-    files=$(globus ls $source_endpoint_id:$dir | grep -E "\.TREFHT\.|\.PRECT" | grep -E "\.h1\.")
-    for file in $files
+        # For MA-HISTORICAL, have to download PRECC and PRECL insrtead of PRECT
+        for i in {1..3}
+        do
+            echo "Listing files in /MA-HISTORICAL.00$i/atm/proc/tseries/month_1... with file pattern \.PRECL\.|\.\PRECC\."
+            files=$(globus ls $source_endpoint_id:/MA-HISTORICAL.00$i/atm/proc/tseries/month_1 | grep -E "\.PRECL\.|\.\PRECC\." | grep -E "\.h0\.")
+            for file in $files
+            do
+                if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
+                    echo "Skipping $file, already exists at destination."
+                else
+                    echo "Transferring $file from /MA-HISTORICAL.00$i/atm/proc/tseries/month_1..."
+                    globus transfer $source_endpoint_id:/MA-HISTORICAL.00$i/atm/proc/tseries/month_1/$file $destination_endpoint_id:$local_destination$file
+                fi
+            done
+        done
+    fi
+fi
+
+# Download daily data as long as user didn't only request monthly data
+if [ "$download_monthly" = false ]; then
+    # Define the file pattern based on the user's selection
+    file_pattern=""
+    if [ "$download_tas" = true ]; then
+        file_pattern="\.TREFHT\."
+    fi
+    if [ "$download_pr" = true ]; then
+        file_pattern="\.PRECT"
+    fi
+    if [ "$download_tas" = false ] && [ "$download_pr" = false ]; then
+        file_pattern="\.TREFHT\.|\.PRECT"
+    fi
+
+    # Download daily TREFHT and/or PRECT files for base_dirs
+    for dir in "${base_dirs[@]}"
     do
-        if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
-            echo "Skipping $file, already exists at destination."
-        else
-            echo "Transferring $file from $dir..."
-            globus transfer $source_endpoint_id:$dir/$file $destination_endpoint_id:$local_destination$file
-        fi
+        # Replace month with day
+        dir=$(echo $dir | sed 's/month_1/day_1/g')
+        echo "Listing files in $dir... with file pattern $file_pattern"
+        files=$(globus ls $source_endpoint_id:$dir | grep -E "$file_pattern" | grep -E "\.h1\.")
+        for file in $files
+        do
+            if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
+                echo "Skipping $file, already exists at destination."
+            else
+                echo "Transferring $file from $dir..."
+                globus transfer $source_endpoint_id:$dir/$file $destination_endpoint_id:$local_destination$file
+            fi
+        done
     done
-done
 
-# Download daily PRECT from ARISE-HISTORICAL
-echo "Listing files in /ARISE-HISTORICAL"
-files=$(globus ls $source_endpoint_id:/ARISE-HISTORICAL | grep -E "\.PRECT\." | grep -E "\.h1\.")
-for file in $files
-do
-    if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
-        echo "Skipping $file, already exists at destination."
-    else
-        echo "Transferring $file from /ARISE-HISTORICAL..."
-        globus transfer $source_endpoint_id:/ARISE-HISTORICAL/$file $destination_endpoint_id:$local_destination$file
+    # Only download if not just downloading tas
+    if [ "$download_tas" = false ]; then
+        # Download daily PRECT from ARISE-HISTORICAL
+        echo "Listing files in /ARISE-HISTORICAL"
+        files=$(globus ls $source_endpoint_id:/ARISE-HISTORICAL | grep -E "\.PRECT\." | grep -E "\.h1\.")
+        for file in $files
+        do
+            if globus ls $destination_endpoint_id:$local_destination | grep -q "^$file$"; then
+                echo "Skipping $file, already exists at destination."
+            else
+                echo "Transferring $file from /ARISE-HISTORICAL..."
+                globus transfer $source_endpoint_id:/ARISE-HISTORICAL/$file $destination_endpoint_id:$local_destination$file
+            fi
+        done
     fi
-done
+fi
\ No newline at end of file
diff --git a/scripts/test_download_gauss.sh b/scripts/test_download_gauss.sh
new file mode 100644
index 0000000..9c046e4
--- /dev/null
+++ b/scripts/test_download_gauss.sh
@@ -0,0 +1,166 @@
+# Configuration
+SCRIPT="./scripts/download_gauss.sh"
+SOURCE_ENDPOINT="test_source_endpoint"
+DEST_ENDPOINT="test_dest_endpoint"
+TEST_DIR="tmp/test"
+
+# Test mutually exclusive flags
+test_mutually_exclusive_flags() {
+    echo "Testing mutually exclusive flags..."
+    
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --tas --pr 2>&1)
+    if ! echo "$output" | grep -q "cannot select both.*tas.*pr"; then
+        echo "✗ Failed to catch mutually exclusive --tas and --pr"
+        return 1
+    fi
+    
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --daily --monthly 2>&1)
+    if ! echo "$output" | grep -q "cannot select both.*daily.*monthly"; then
+        echo "✗ Failed to catch mutually exclusive --daily and --monthly"
+        return 1
+    fi
+    
+    echo "✓ Mutually exclusive flags tests passed"
+}
+
+test_file_patterns() {
+    echo "Testing file pattern generation..."
+    
+    # Test TAS + MONTHLY 
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --tas --monthly 2>&1)
+    if echo "$output" | grep -q "TREFHT" && echo "$output" | grep -q "month_1" && ! echo "$output" | grep -q "PRECT\|PRECL\|PRECC\|day_1"; then
+        echo "✓ Test passed for --tas --monthly pattern."
+    else
+        echo "✗ Test failed for --tas --monthly pattern."
+        return 1
+    fi
+    
+    # Test PR + MONTHLY
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --pr --monthly 2>&1)
+    if echo "$output" | grep -q "PRECT" \
+       && echo "$output" | grep -q "PRECL\|PRECC" \
+       && echo "$output$" | grep -q "month_1" \
+       && ! echo "$output" | grep -q "TREFHT\|day_1"; then
+        echo "✓ Test passed for --pr --monthly pattern."
+    else
+        echo "✗ Test failed for --pr --monthly pattern."
+        return 1
+    fi
+        
+    # Test TAS + DAILY
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --tas --daily 2>&1)
+    if echo "$output" | grep -q "TREFHT" \
+       && echo "$output" | grep -q "day_1" \
+       && ! echo "$output" | grep -q "PRECT\|ARISE\|month_1"; then
+        echo "✓ Test passed for --tas --daily pattern."
+    else
+        echo "✗ Test failed for --tas --daily pattern."
+        return 1
+    fi
+
+    # Test PR + DAILY
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --pr --daily 2>&1)
+    if echo "$output" | grep -q "PRECT" \
+       && echo "$output" | grep -q "day_1" \
+       && echo "$output" | grep -q "ARISE" \
+       && ! echo "$output" | grep -q "TREFHT\|month_1"; then
+        echo "✓ Test passed for --pr --daily pattern."
+    else
+        echo "✗ Test failed for --pr --daily pattern."
+        return 1
+    fi
+
+    # Test TAS only
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --tas 2>&1)
+    if echo "$output" | grep -q "TREFHT" \
+       && echo "$output" | grep -q "day_1" \
+       && echo "$output" | grep -q "month_1" \
+       && ! echo "$output" | grep -q "PRECT\|ARISE"; then
+        echo "✓ Test passed for --tas pattern."
+    else
+        echo "✗ Test failed for --tas pattern."
+        return 1
+    fi
+
+    # Test PR only
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --pr 2>&1)
+    if echo "$output" | grep -q "PRECT" \
+       && echo "$output" | grep -q "day_1" \
+       && echo "$output" | grep -q "month_1" \
+       && echo "$output" | grep -q "ARISE" \
+       && echo "$output" | grep -q "PRECL\|PRECC" \
+       && ! echo "$output" | grep -q "TREFHT"; then
+        echo "✓ Test passed for --pr pattern."
+    else
+        echo "✗ Test failed for --pr pattern."
+        return 1
+    fi
+
+    # Test MONTHLY only
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --monthly 2>&1)
+    if echo "$output" | grep -q "PRECT" \
+       && echo "$output" | grep -q "PRECL\|PRECC" \
+       && echo "$output" | grep -q "TREFHT" \
+       && echo "$output$" | grep -q "month_1" \
+       && ! echo "$output" | grep -q "day_1\|ARISE"; then
+        echo "✓ Test passed for --monthly pattern."
+    else
+        echo "✗ Test failed for --monthly pattern."
+        return 1
+    fi
+
+    # Test DAILY only
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR --daily 2>&1)
+    if echo "$output" | grep -q "PRECT" \
+       && echo "$output" | grep -q "TREFHT" \
+       && echo "$output$" | grep -q "ARISE" \
+       && echo "$output$" | grep -q "day_1" \
+       && ! echo "$output" | grep -q "PRECL\|PRECC\|month_1"; then
+        echo "✓ Test passed for --daily pattern."
+    else
+        echo "✗ Test failed for --daily pattern."
+        return 1
+    fi
+
+    # Test with no patterns
+    output=$($SCRIPT $SOURCE_ENDPOINT $DEST_ENDPOINT $TEST_DIR 2>&1)
+    if echo "$output" | grep -q "PRECT" \
+       && echo "$output" | grep -q "TREFHT" \
+       && echo "$output" | grep -q "PRECL\|PRECC" \
+       && echo "$output$" | grep -q "ARISE" \
+       && echo "$output$" | grep -q "day_1" \
+       && echo "$output$" | grep -q "month_1"; then
+        echo "✓ Test passed for no pattern (original function)."
+    else
+        echo "✗ Test failed for no pattern (original function)."
+        return 1
+    fi
+}
+
+
+# Main test runner
+main() {
+
+    # Run all tests
+    tests=(
+        test_mutually_exclusive_flags
+        test_file_patterns
+    )
+    
+    failed=0
+    for test in "${tests[@]}"; do
+        if ! $test; then
+            failed=$((failed + 1))
+        fi
+    done
+
+    # Report results
+    total=${#tests[@]}
+    passed=$((total - failed))
+    echo "Test Results: $passed/$total tests passed"
+    
+    return $failed
+}
+
+# Run the test suite
+main "$@"
\ No newline at end of file