The number of overnight camping stays in U.S. national parks has declined in the past 15 years, the Associated Press reported.

More than 9.2 million overnight camping stays were recorded in America’s national parks 15 years ago in 1998. The number dropped to 8.54 million five years later in 2003; 7.99 million five years after that in 2008, and 7.91 million last year, in 2013.

The statistics include tent camping as well as RVs, backcountry camping and stays in campgrounds operated by concessions.

National Park Service spokesman Jeffrey Olson said the decline began in the mid-1990s but began to level out around 2004. The numbers do fluctuate from year to year, however, with some years showing increases.

Camping and overall park visitation is affected by everything from the weather to the economy.

In 2013, visitation to national parks was hurt by the government shutdown in October. Overall national park visits were down 3% in 2013 from 2012, so it’s not surprising that camping stays dropped as well, from nearly 8.4 million in 2012 to last year’s 7.9 million.

But in 2002, the year after the Sept. 11th attacks, when some travellers chose drive-to destinations over air travel, camping numbers were robust, with 8.7 million camping stays in the parks — though still lower than in 1998.

Camping numbers spiked in 2009 and 2010 as well, to more than 8.5 million each year, when the weak economy may have encouraged some travellers to stay closer to home rather than buying plane tickets.

Olson says more lodging options near parks is also a major factor in the long-term decline. Gateway communities have become savvier about offering hotels, motels, food and entertainment to visitors heading into the parks. It’s become easier for visitors to spend the day inside a park and then get a comfy bed, maybe with Wi-Fi and cable TV, at night in a nearby town.

Olson added that in the biggest, most famous and most-visited parks in the system, “camping is still very popular,” with numbers down only slightly and campgrounds often at capacity. But in smaller, less well-known parks, camping numbers are off as much as 30%.

Bad weather — ranging from hurricanes to wildfires — also affects numbers, both by closing parks and keeping people home.

Studies conducted by the Outdoor Foundation, which promotes outdoor recreation for the industry, have also shown year-over-year declines in camping. A 2013 report sponsored by the foundation and the Coleman Co. cited “a lack of time due to work and family commitments” as the No. 1 reason for the reduction.

Olson agreed, saying “the two-week vacation has gone by the wayside.”